<< Click to Display Table of Contents >> Navigation:  Using SyncBackPro > Technical Reference > Common Errors and What They Mean

 

This page lists the error messages most commonly reported by SyncBackPro users, what they usually mean, and the first checks to perform. It is not a substitute for the profile log. If a profile fails, open the log first and note the exact message, whether the failure happened on the source or the destination, and whether the profile was run manually or by the Windows Task Scheduler.

 

Many of these errors are returned by Windows, the Task Scheduler antivirus software, your NAS, or the file system. The wording in the log reflects what the underlying component reported, not what SyncBackPro itself decided.

 

Use your browser's find feature to search for an exact error message, or browse by category.

 

 

Where to Find the Error

 

•Right-click the profile in the main window and choose View log. See the Log page for details on log settings.

•For scheduled profiles, also open Windows Task Scheduler and check the History tab for the task. See Scheduling Problems.

•For diagnostic information to send to support, use the Technical Support Wizard.

 

 

1. Access is denied / Error 5 / 0x80070005

 

Common messages

 

•Access is denied

•Error 5: Access is denied

•0x80070005 - Access is denied

•DeleteFile failed; code 5 Access is denied

•Read Only (added by SyncBackPro when a delete fails on a read-only file)

•Cannot clear read-only flag

•Security settings could not be set: ...

•Security settings could not be read: ...

•Scan failed ... error code 13 (SyncBack Touch on Android)

 

What it means

 

Windows is refusing to give SyncBackPro the access it needs. The most common reasons are NTFS file permissions, the read-only attribute, network share permissions, the Windows account SyncBackPro is running as, and security software. Where SyncBackPro can identify a specific cause (such as the read-only flag) it will say so.

 

Likely causes

 

•The file has the read-only attribute set, and the profile is not configured to clear it.

•The Windows account running SyncBackPro does not have read permission on the source, or write/delete permission on the destination.

•The destination volume is mounted read-only (BitLocker recovery, ChkDsk failure, USB write-protect switch).

•Network share permissions and NTFS file-system permissions do not both allow access.

•SyncBackPro is running elevated, as a different user, or via a scheduled task using different credentials from when you tested manually.

•Copying NTFS owner or audit security entries requires SeRestorePrivilege and SeSecurityPrivilege. Without these, security copy fails.

•The file is encrypted with Windows EFS by another user (see Decryption).

•Antivirus or endpoint protection is blocking access.

•A NAS device may reject the temporary rename used by safe copy. See the NAS section.

•The path is System Volume Information, which Windows protects and which should normally be excluded.

•Windows Defender Controlled Folder Access (part of ransomware protection) blocks unrecognised apps from writing to protected folders such as Documents, Pictures, Videos, Music, Desktop, and Favorites. The same file may be writable in Explorer because Explorer is on the allowed list and SyncBackPro is not.

 

First checks (in order)

 

•Confirm whether the error is on the source or destination side. The log will say.

•If the message includes Read Only, clear the read-only attribute or enable Clear the read-only attribute before delete on the Copy/Delete page.

•Run SyncBackPro elevated for system and Program Files locations.

•On the destination, confirm the Windows account has Modify rights on the folder.

•For scheduled tasks, confirm the right account is in use and that Do not store password was not enabled inadvertently.

•If Security settings could not be set/read appears, either run elevated or disable Copy NTFS security permissions on the Compare Options, Security page.

•If the destination is in Documents, Pictures, Videos, Music, Desktop, Favorites, or another folder protected by Controlled Folder Access, open Windows Security » Virus & threat protection » Ransomware protection » Allow an app through Controlled folder access, and add the SyncBackPro executable (and any helper executables such as the Scheduler Monitor Service) to the allowed list.

• Do not unblock or allow files flagged by your security software unless you are certain the file is safe.

 

Read more

 

•In this help file: Copy/Delete, Locked, Copy/Delete, Advanced, Administrator Protection.

•On the 2BrightSparks site: A basic introduction to NTFS permissions, SyncBack Elevation, Administrator Protection (Windows 11).

 

 

2. The drive X does not exist / Network path unavailable

 

Common messages

 

•The drive X: does not exist!

•No disk in drive X:

•Drive 'X' was removed during scan

•Directory does not exist: ...

•Directory X does not exist and cannot be created

•A network drive works when run manually, but fails when run by the scheduler.

 

What it means

 

The drive letter, network path, or folder was not present at the moment SyncBackPro tried to use it, or it disappeared partway through the scan. This is very common with mapped drive letters, with USB drives that received a different letter on the next reboot, and with NAS shares that drop their connection on idle.

 

Likely causes

 

•Mapped drive letters are specific to the Windows session that created them. A different session, including a scheduled task, will not see them.

•An elevated SyncBackPro cannot see drives mapped by a non-elevated Explorer, and vice-versa.

•A USB or removable drive has been assigned a different drive letter, unplugged, or has lost power.

•The optical drive is empty.

•The destination folder was renamed or deleted.

•A variable used in the path expanded to an empty string at run time.

•A network share dropped during the scan, or the laptop went to sleep (USB power-saving can disconnect drives on battery).

 

First checks

 

•Replace mapped drive letters in the profile with UNC paths such as \\server\share\folder\.

•For a USB or removable drive that receives a different letter each time it is plugged in, replace the drive letter in the profile's source or destination with the %SERIAL% or %LABEL% variable. SyncBackPro will then locate the correct drive by its volume serial number or volume label regardless of which letter Windows has assigned. For example: %SERIAL=1234-ABCD%\Backups\ or %LABEL=MyBackup%\Backups\. See Variables for the full syntax.

•Trigger profiles on drive insertion rather than a scheduled time for removable media.

•As a Windows-side alternative, assign a fixed drive letter to the removable drive in Windows Disk Management.

•If credentials are needed for a network path, set them on the profile's Network page.

•If the path already uses a variable that may be empty at run time, see the Variables page to verify what it resolves to.

 

Read more

 

•In this help file: Copy/Delete, Network, Network.

•On the 2BrightSparks site: Windows drive letter changes.

 

 

3. Scheduled task does not run

 

Common messages

 

•Scheduled task does not run, or runs with no log produced.

•0x80070005 - Access is denied

•The operator or administrator has refused the request (0x800710E0)

•Profile cannot be found when run by the scheduler.

•Task works manually but not unattended.

 

What it means

 

Windows Task Scheduler is unable to start the profile, or starts it under conditions where it cannot find what it needs (profiles, log folder, mapped drives, network credentials).

 

Likely causes

 

•Wrong Windows username or password.

•The user entered a Windows Hello PIN instead of the Windows login password.

•Blank-password restrictions prevent the task from running.

•The task runs as a different Windows account from the one that owns the profiles. Profiles are user-specific.

•The task runs as SYSTEM or SERVICE and cannot find user-specific profile storage.

•The task is configured not to run unless the user is logged on.

•The task is disabled, or is already running with policy Do not start a new instance.

•Network credentials are not available because the task is configured not to store the password.

 

First checks

 

•Confirm the task user account.

•Confirm the password is the Windows account password, not a PIN.

•Confirm the profile exists for that user.

•Confirm the log-storage location is accessible to the account.

•Confirm the task is enabled and check the History tab in Task Scheduler.

•If the task looks corrupted, delete it and recreate the schedule from inside SyncBackPro.

 

Read more

 

•In this help file: Scheduling Problems, Scheduler Monitor Service, Command Line Parameters.

•On the 2BrightSparks site: Windows Task Scheduler.

 

 

4. Open or locked files / VSS errors

 

Common messages

 

•File is locked: <name>

•File is being locked by: <application> (SyncBackPro uses Windows Restart Manager to identify the application where possible)

•Sharing violation (Win32 error 32)

•Creating the Shadow Volume took too long - open/locked files cannot be copied

•Unable to create shadow volume: Initialization failure

•VSS_E_BAD_STATE

•External exception E06D7363 when copying open or locked files.

 

What it means

 

Either another program is holding the file open and not sharing read access, or the Volume Shadow Copy Service (VSS) that SyncBackPro uses to read open files could not produce a snapshot. Where SyncBackPro can identify the locking application via the Windows Restart Manager, it will name it.

 

Likely causes

 

•Desktop search, antivirus, a database, an email client, or another application is holding the file open.

•SyncBackPro does not have the privileges required to create or use VSS snapshots.

•Another backup product has VSS in use.

•There is not enough free space on the snapshotted volume (VSS needs roughly 10 percent for its shadow copy area).

•32-bit SyncBackPro is running on 64-bit Windows. VSS is only fully supported in the 64-bit build.

•One or more Windows VSS writers are in a failed or waiting state.

•The Scheduler Monitor Service is not installed or not available.

•Windows updates or vulnerable-driver blocklist changes have disturbed VSS providers.

 

First checks

 

•Close the application named in the File is being locked by message, if any.

•Enable VSS for open files on the Copy/Delete, Locked page. VSS requires administrator privileges and an NTFS source.

•Use the 64-bit SyncBackPro build for full VSS support.

•Enable Retry on failure with a short delay on the Copy/Delete, Advanced page for transient locks such as antivirus scanning.

•From an elevated command prompt, run vssadmin list writers and look for any writer not in Stable / No error. Run vssadmin list providers to check for broken providers, and vssadmin resize shadowstorage to enlarge the shadow copy area if needed.

•Reboot the machine to clear stuck VSS writers, then retry.

 

Read more

 

•In this help file: Open and Locked File Copying, Copy/Delete, VSS, Copy/Delete, Locked.

•On the 2BrightSparks site: Locked files, Volume Shadow Copy (VSS), Understanding file attributes.

 

 

5. Safe copy failed / Failed to rename temp file

 

Common messages

 

•Safe copy failed

•Failed to rename temp file

•Cannot move file (3): The system cannot find the path specified

•File does not exist

 

What it means

 

Safe copy writes the destination file under a temporary name first and then renames it. Either the temporary file vanished before the rename, or the destination did not allow the rename.

 

Likely causes

 

•Antivirus or anti-malware quarantines or deletes the temporary file before SyncBackPro can rename it.

•Security tools detect executable or script content even when the temporary file has an anonymous name.

•A NAS or network device handles temporary files or renames differently from local NTFS. See the NAS section.

•Verification may fail if the file disappears before hashing.

 

First checks

 

•Check antivirus and security logs at the time the profile failed.

•Safe copy writes to a temporary file and then renames it, to reduce the risk of a corrupted partial copy. Disabling safe copy may avoid the temporary-name issue but will not address an underlying quarantine, and removes the corruption-prevention benefit.

 

Read more

 

•In this help file: Copy/Delete, Advanced.

 

 

6. NAS-specific errors and quirks

 

Many NAS devices present themselves as NTFS-like SMB shares but behave differently in subtle ways. SyncBackPro already includes workarounds for most of the known quirks, but if your NAS is reporting odd errors it can be worth knowing what each one means.

 

Common messages

 

•The drive or device is incorrectly stating the file exists when it does not. SyncBackPro will append a recommendation to update the NAS firmware and scan the NAS for disk errors.

•ERROR_ACCESS_DENIED when deleting a file that has the read-only flag set, even though the same account can delete other files in the same folder.

•ERROR_INVALID_FUNCTION during large-fetch directory enumeration.

•ERROR_INVALID_LEVEL or ERROR_EAS_NOT_SUPPORTED when creating a folder.

•ERROR_INVALID_PARAMETER (87) returned intermittently. SyncBackPro already retries this up to 5 times automatically.

•ERROR_ALREADY_EXISTS (183) when the file should not exist.

•The router or provider is busy, possibly initializing. The caller should retry

•There are open files so the networked drive cannot be disconnected

•Folder listings contain duplicate entries.

•File timestamps are rounded to 2-second precision (FAT-style) instead of NTFS precision.

•Connection to the NAS is dropped while a profile is running, then comes back.

•On ASUStor with Btrfs, the parent folder of a newly-created folder appears with unexpected attributes.

 

What it means

 

The NAS firmware's SMB server implements a subset of the Windows file API, and edge cases are not always handled the same way. The errors above are returned by Windows, but the cause is the NAS firmware. SyncBackPro retries, ignores, or reinterprets many of these silently.

 

First checks

 

•Update the NAS firmware and scan the NAS for disk errors.

•Use UNC paths, not mapped drive letters, especially for scheduled profiles.

•On the Network page, consider enabling Connect to share first.

•On the Network, Advanced page, enable Do not disconnect after profile run for the source or destination.

•If scans fail with ERROR_INVALID_FUNCTION, disable Use large FindFirst cache in the TreeScan options on the Copy/Delete, Network page.

•For timestamp drift, enable Ignore time differences of 2 seconds or less on the Compare Options, Date Time page. This is recommended for any non-NTFS destination.

•If the share goes to sleep, use Wake-on-LAN as a Before profile step, or disable NAS sleep.

 

Read more

 

•In this help file: Copy/Delete, Network, Network, Network, Advanced, Compare Options, Date Time.

•On the 2BrightSparks site: NAS backup best practices, What is the SMB protocol, Network file systems.

 

 

7. Cloud authorisation, quota, and provider API errors

 

Common messages

 

•rateLimitExceeded (Google Drive)

•Quota exceeded for drive.googleapis.com

•403 Forbidden - Access Denied

•Expired or invalid Azure SAS URL.

•HTTP 404 Not Found during large-file download from SharePoint or OneDrive.

•Egnyte 403 authorisation or scopes error.

•Google Drive requires your own client ID and client secret.

•

What it means

 

The cloud provider has refused the request. The most common reason is an OAuth token that has expired, been revoked, or never had the right scopes. The second most common reason is a quota or rate limit on the shared API credentials.

 

First checks by provider

 

•Google Drive: configure your own client ID and client secret, re-authorise the linked account, and check rate limits. See Google Drive.

•OneDrive and SharePoint: re-authorise, confirm site and library selection. Large-file download URLs can expire mid-transfer.

•Amazon S3 (and S3-compatible / Lightsail): verify endpoint, region, access key and secret, storage class, and ACL.

•Microsoft Azure: check the SAS URL or access key. A cold or archive blob must be rehydrated before it can be read.

•Egnyte: confirm required scopes are granted by an Egnyte administrator.

•Gmail (log notifications and email backup): re-authorise the Gmail account; ordinary passwords no longer work.

 

Re-authorise the linked cloud account before changing other profile settings. That is the usual fix for 403, 401, and expired-token errors.

 

Read more

 

•In this help file: Cloud, Cloud, Advanced, Upgrading Cloud Service, Secrets Manager.

•On the 2BrightSparks site: OAuth 2, Google Drive OAuth, Gmail OAuth, Google Drive client ID.

 

 

8. Ransomware detection halted the backup

 

Common messages

 

•The contents of the ransomware detection file have changed.

•Ransomware infection detected on the source/left.

•Ransomware infection detected on the destination/right.

•No profiles can be run because ransomware was detected on this system. (Global Settings)

•SyncBack Touch reports a ransomware infection.

 

What it means

 

SyncBackPro uses a detection file (sometimes called a canary file) to detect ransomware. You point SyncBackPro at an existing file of 1 MiB or smaller on the location you want monitored. At each run SyncBackPro reads that file and calculates its hash. If the hash differs from the recorded value, SyncBackPro treats it as evidence of a ransomware infection and refuses to run, on the assumption that the file should not have been altered by anything legitimate.

 

This is a separate mechanism from the TooManyDeletes / TooManyCopies / TooManyUpdates safety thresholds (see section 17). Those abort when the planned file operation count exceeds the configured percentage. A large TooManyDeletes figure can be a symptom of ransomware, but it is not the detection-file mechanism described here.

 

The three scopes

 

•Global Settings: the detection file lives on the local system SyncBackPro is running on. If its hash changes, no profiles run.

•SyncBack Touch: the detection file lives on the remote Touch device. If its hash changes, no profile that uses that Touch service runs.

•Profile-level: a detection file can be configured per source/left and per destination/right. If its hash changes, this profile will not run.

 

All three scopes work independently and can be used together.

 

First checks

 

• Do not immediately pick a new detection file and rerun. Find out first why the hash of the existing one changed.

•Inspect the file you nominated as the detection file. Was it edited, replaced, restored from backup, moved, or renamed? Any of these will change its hash even if there is no ransomware.

•If you believe ransomware is present, treat the affected location as compromised. The destination copy from the last good run is your recovery source.

•If the change was legitimate, choose a new stable, low-traffic existing file on the Ransomware Detection page so SyncBackPro can record a fresh hash.

•Make sure the detection file is excluded from the profile's own copy. Otherwise the profile itself may overwrite or remove it. Use filters or deselect it on the Sub-directories and Files page.

•The detection file must be 1 MiB (1,048,576 bytes) or smaller.

• For cloud destinations, do not nominate a file in cold storage (for example Glacier or Azure Archive). Retrieval cost and delay make it impractical and the file may be effectively immutable.

 

Read more

 

•In this help file: Ransomware Detection (profile-level), Global Settings » Ransomware (local system), SyncBack Touch » Ransomware (Touch device).

•On the 2BrightSparks site: Ransomware detection with SyncBack, Ransomware-resilient backups, Protect yourself from ransomware.

 

 

9. I/O error 112 / Not enough disk space

 

Common messages

 

•Exception in RunTheProfile - 112

•I/O error 112

•The drive X may be full or read-only

•Warning! You do not have enough free disk space on '...'.

 

What it means

 

Windows refused a write because the target volume is out of space, or SyncBackPro's pre-run check estimated the copy needs more space than is available. The target is not always the destination drive. The Windows temporary folder and the profile log folder also need free space. The pre-run estimate is based on listed file sizes; actual usage may differ slightly because of compression and sparse files.

 

First checks

 

•Check free space on the destination, the source, the Windows %TEMP% folder, and the SyncBackPro profile-storage folder.

•Confirm the destination volume is not mounted read-only.

•Compression and verification can temporarily need more free space than the final file.

•If old versions are filling the destination, review your retention rules on the Versioning page, then remove known unwanted versions manually rather than relying on bulk deletion.

• Before running any profile or cleanup that enables deletes against the destination, do a simulated run first and review the Differences window so you can see exactly what would be removed.

 

Read more

 

•In this help file: Versioning, Log.

•On the 2BrightSparks site: Fix not enough space on Windows when copying files.

 

 

10. Antivirus or potentially unwanted software warnings

 

Common messages

 

•Operation did not complete successfully because the file contains a virus or potentially unwanted software

•Access denied while copying profile, log, or history files.

•A safe-copy temporary file disappears mid-copy.

 

What it means

 

SyncBackPro is relaying an error from Windows Defender or another security product. SyncBackPro does not scan files for viruses itself.

 

First checks

 

•Check Windows Security or your antivirus logs around the time of the failure.

•If Access Denied appears for files in Documents, Pictures, Videos, Music, Desktop, Favorites, or other protected folders, check whether Windows Defender Controlled Folder Access is blocking SyncBackPro. See section 1 for the steps to allow SyncBackPro through Controlled Folder Access.

• Do not add SyncBackPro, the source files, or the destination to an antivirus exclusion list unless you are certain the files are safe and you understand the security implications.

 

 

11. Copy, move, and delete errors (Windows error codes)

 

Copy, move, and delete errors all include the underlying Windows error code in parentheses, followed by the Windows description. Examples: Cannot copy file (5): Access is denied, Cannot move file (32): The process cannot access the file because it is being used by another process. The most common codes and their fixes are listed below.

 

 

Cannot create hard link / symbolic link

 

The destination file system does not support links (FAT, exFAT, and many NAS shares cannot), or the account lacks SeCreateSymbolicLinkPrivilege for symlinks. Switch to a regular copy, choose an NTFS destination, or run elevated. See Copy/Delete, Links.

 

Failed to set short filename

 

The destination volume has 8.3 short-name generation disabled, is not NTFS, or the chosen short name conflicts. Disable Set the short filename on the Compare Options, Attributes page if 8.3 names are not actually needed.

 

 

12. Date and time errors

 

Common messages

 

•Cannot get date and time of file

•Cannot get date and time from server: ...

•Failed to change modification date-time: ... (also creation, last access)

•Cannot set modification date and time for file on FTP server

 

Likely causes

 

•FAT precision rounds modification times to 2-second multiples on even seconds.

•The FTP server does not implement MDTM set, MFMT, or MFCT. Many older or restricted-permission FTP servers do not.

•The NAS firmware does not honour SetFileTime.

•The destination is read-only.

•The source file has an invalid or out-of-range modification date.

 

First checks

 

•Enable Ignore time differences of 2 seconds or less on the Compare Options, Date Time page. Recommended for any non-NTFS destination including most NAS shares.

•Disable Set the modification date-time on the destination if it is not actually needed.

•On the FTP, Advanced page, try a different MDTM syntax, or enable Calculate time-zone offset.

•For local files with a bad date, check the file in Explorer and correct it at the source.

 

 

13. Filename and path length errors

 

Common messages

 

•The filename may be too long

•The Zip filename is too long (maximum length is N characters)

•FILENAME_EXCED_RANGE (Win32 error 206)

•DOS filters must be shorter than N characters

•Invalid Windows filename when syncing from FTP, SFTP, or cloud sources.

•A file or folder is ignored because it already exists under the same name with a different case.

 

Likely causes

 

•The path exceeds MAX_PATH (260 characters) on a destination that does not support long paths.

•Zip 2.0 has an internal 256-character filename limit.

•Windows is case-insensitive but a remote system (Linux, FTP, cloud) presents names that differ only by case.

•A remote system allows characters that Windows does not (such as colon or question mark).

•Junctions or mount points cause the scan to recurse back into a folder it has already processed.

 

First checks

 

•Enable long path support in Windows (registry value LongPathsEnabled=1).

•Switch from Zip 2.0 to Zip 64 on the Compression page.

•Move the source folder higher in the tree to shorten relative paths.

•For DOS filter length, switch to regular expressions or split the filter into multiple lines on the Filter Settings page.

•Review junction and link handling on the Copy/Delete, Links page.

 

 

14. Verification and integrity errors

 

Common messages

 

•The file cannot be verified: ...

•Cannot retrieve file integrity hash from <source/destination>

 

Likely causes

 

•The destination file changed between write and read-back (antivirus scanning, indexer touching metadata).

•The source file changed during the copy (live database file or similar).

•The integrity database is locked, corrupt, or unreachable.

 

First checks

 

•Check antivirus or endpoint protection logs around the time of the failure. If real-time scanning is modifying files during verification, consider a folder exclusion for SyncBackPro's destination, but only if the files are known safe and your security policy permits it (see section 10).

•Use VSS to snapshot the source for files that change frequently.

•Enable retry on verification mismatch.

•On the Integrity Check page, clear the integrity database or move it to a local drive. Cloud-stored integrity databases are slow and error-prone.

 

 

15. SMB and network-share errors

 

Common messages

 

•Access to the network resource was denied

•The network path was not found

•The remote name (...) is not acceptable to any network resource provider

•The local device specified is already connected to a network resource

•There is no network present

•The user name or password is incorrect

•Logon failure: unknown user name or bad password

 

What it means

 

Windows could not connect to, authenticate to, or reach the SMB/CIFS share that the profile uses. The error comes from the Windows network redirector, not from SyncBackPro.

 

Likely causes

 

•Username or password rejected, or share-level permissions exclude this account.

•Share permissions and NTFS permissions disagree. Both must allow access.

•For scheduled tasks running as SYSTEM, the share needs to permit the computer account (DOMAIN\HOSTNAME$). Most home NAS will not. Run the task as a real user instead.

•Server name or share name typo, DNS resolution failure, or the share is offline.

•A mapped drive letter is already in use by a different share (often a different session's view of the same letter).

•No network adapter is up, or the connection profile is Public with sharing disabled.

•SMB protocol version mismatch. Some older NAS devices only speak SMB1, which Windows 10 and 11 disable by default.

 

First checks

 

•Re-enter credentials on the Network page.

•Use UNC paths rather than mapped drive letters. Using network drive letters is not recommended.

•Ping the host, try the IP address directly, and check the firewall (SMB ports 139 and 445).

•Open the share manually in Explorer using the same account that SyncBackPro will run as. If Explorer also fails, the issue is Windows-side, not SyncBackPro-side.

• Only enable the SMB1 client in Windows Features as a temporary workaround. Update the NAS firmware to SMB2 or higher instead. SMB1 has known security vulnerabilities.

 

Read more

 

•In this help file: Network, Network, Advanced, Copy/Delete, Network. NAS-specific quirks are in section 6.

•On the 2BrightSparks site: What is the SMB protocol, Network file systems.

 

 

16. FTP and SFTP errors

 

Common messages (FTP and FTPS)

 

•530 Login authentication failed, 530 Not logged in

•Cannot connect to FTP server / Connection timed out

•Socket Error 11001 - Host not found

•Socket Error 11004 - Unable to connect (usually leading/trailing spaces in the host, or a ftp:// URL where a bare hostname is expected)

•Socket Error 10061 - Connection refused

•Socket Error 10054 (with FTPS, typically Windows Firewall stateful FTP inspection)

•Cannot enter passive mode / PASV command not accepted

•Cannot select destination directory

•421 Service not available, closing control connection

•421 Too many connections from this IP

•425 Cannot open data connection / 425 Unable to build data connection: Operation not allowed

•426 Connection closed; transfer aborted

•450 TLS session of data connection has not resumed or the session does not match the control connection

•451 Failure writing to local file

•522 SSL connection failed; session reuse required

•550 Data channel timed out

•550 The supplied message is incomplete. The signature was not verified.

•SSL/TLS handshake failed / Certificate could not be verified

•Cannot retrieve directory listing / Cannot parse directory listing

•Cannot get date and time from server

•Cannot set modification date and time for file on FTP server

 

Common messages (SFTP)

 

•Host key verification failed / Host key has changed

•No matching host key type, No supported authentication methods

•Unable to load SFTP key (...): ...

•Permission denied (publickey)

•Server unexpectedly closed the connection

 

What it means

 

The remote FTP, FTPS, or SFTP server refused or could not complete the request. The cause is usually authentication, firewall and data-channel routing, TLS configuration, server feature support, or (for SFTP) host-key trust.

 

Likely causes

 

•Login (530): wrong username or password, the account is disabled, or the account is not allowed to access this directory.

•Connection timeout: the server is unreachable, the control port is blocked, or the server is offline.

•Passive vs active mode: the profile's mode does not match what the server, your firewall, or NAT allows. Most home and office networks need passive mode. Active mode requires inbound connections to the client.

•TLS/SSL handshake: the profile is configured for plain FTP but the server requires explicit FTPS, or vice-versa; the server certificate is expired, self-signed, or the hostname does not match; the server requires a TLS version or cipher that is disabled at one end.

•Directory listing parse failure: the server returns a LIST output in a non-standard format that SyncBackPro cannot recognise.

•Date and time on server: the FTP server does not implement MDTM set, MFMT, or MFCT. See also section 12.

•Windows Firewall stateful FTP inspection (Socket 10054 with FTPS): Windows Firewall's stateful FTP inspection cannot read encrypted FTPS control commands and can drop the connection.

•FTP engine compatibility (425, 450 with specific servers): the default FTP engine does not always negotiate correctly with every server. Known cases include 425 Unable to build data connection with ProFTPD, and 450 TLS session of data connection has not resumed with FileZilla Server 0.9.51 or newer.

•Server-side resource limits and storage: 421 Too many connections from this IP indicates the server's per-IP connection limit was exceeded. 451 Failure writing to local file means the server cannot store the upload, typically because of disk space, user quota, or folder permissions.

•Server certificate cipher and TLS version restrictions: some Windows FTPS servers produce 550 The supplied message is incomplete. The signature was not verified. when their TLS cipher priority or TLS version configuration is incompatible with the client.

•Windows update side-effects (522): certain Windows updates have changed SSL session-reuse behaviour and triggered 522 SSL connection failed; session reuse required against servers (such as vsftpd) that require session reuse.

•SFTP host key changed: the server's host key is not the one previously trusted. Either the server was legitimately rebuilt or migrated, or the connection is being intercepted.

•SFTP key authentication: the key file is in an unrecognised format (OpenSSH versus PuTTY .ppk), the passphrase is wrong, the public key is not in authorized_keys on the server, or the file or its containing folder is world-readable.

 

First checks

 

•For login failures, re-enter the username and password on the FTP page. Confirm the account has access to the working directory.

•For connection timeouts, try the host name then the IP address. Check that the control port is open: 21 for FTP/FTPS-explicit, 990 for FTPS-implicit, 22 for SFTP.

•Switch between passive and active mode on the FTP, Advanced page. For active mode behind a router or firewall, see FTP, Firewall.

•For TLS errors, confirm the connection mode on the FTP page matches what the server expects (plain FTP, explicit FTPS, or implicit FTPS). On the FTP, Advanced page, review certificate validation options.

•For directory listing parse failures, enable debug output so the raw LIST output is captured, then send the log to support.

•For FTP date issues, disable Set modification date/time on destination, or enable Calculate time-zone offset on the FTP, Advanced page.

•For 425 Unable to build data connection (ProFTPD) or 450 TLS session of data connection has not resumed (FileZilla Server), switch the FTP engine on the FTP page to the alternative engine (WeOnlyDo). Alternatively, on the FileZilla Server side, disable Require TLS session resumption on data connection.

•For Socket Error 10054 with FTPS, either disable Windows Firewall stateful FTP inspection with netsh advfirewall set global StatefulFtp disable from an elevated command prompt, or switch the profile to implicit FTPS.

•For 421 Too many connections from this IP, reduce Scan threads and Worker threads on the FTP, Advanced page, or raise the server's per-IP connection limit.

•For 451 Failure writing to local file and 550 Data channel timed out, the problem is on the FTP server side (disk space, user quota, folder permissions, or firewall configuration on the server's passive-port range). Contact the server administrator.

• For SFTP host key changed, do not accept the new key blindly. Verify out of band (e.g. by asking the server's administrator) that the change was legitimate before trusting it. An unexpected host key change can indicate a man-in-the-middle attack.

•For SFTP key authentication failures, convert keys with PuTTYgen when mixing OpenSSH and PuTTY tooling, re-enter the passphrase, and confirm the private key file is not world-readable. On the server, confirm the public key is present in the user's authorized_keys file.

 

Read more

 

•In this help file: FTP, FTP, Advanced, FTP, Proxy, FTP, Firewall, FTP, HTTP.

•2BrightSparks Knowledge Base, FTP error reference: Common FTP errors and Socket Error messages, Active versus Passive for FTP, 421 Too many connections from this IP, 425 Unable to build data connection, 450 TLS session of data connection has not resumed, 451 Failure writing to local file, 522 SSL connection failed, 550 Data channel timed out, 550 The supplied message is incomplete.

 

 

17. Profile aborted: Why?

 

When a profile aborts, SyncBackPro records an explicit reason. The reason appears in the log and in the result row in the main window. The most common reasons are listed below.

 

•User: you clicked Abort, or another instance asked SyncBackPro to stop.

•TooManyDeletes: pre-run check found more files queued for deletion than the configured threshold. Safety abort.

•TooManyCopies: same, for copies and moves.

•TooManyUpdates: same, for updates.

•TooManyErrors: more errors than the configured threshold.

•TimeUp: the time limit was reached.

•WindowsShutdown: Windows is shutting down.

•ProgramClose: SyncBackPro itself is closing.

•Script: a user script raised an abort.

•StoppingGroup: the parent group queue was stopped.

 

First checks for TooMany... aborts

 

•Review the planned changes in the differences window before clicking Continue Run.

•If the action was intended, raise the warning threshold on the Copy/Delete, Warning page.

•If not, tighten filters and decisions and re-run.

• A large TooManyDeletes abort may indicate ransomware activity. See section 8.

 

 

18. Profile and settings cannot be saved, loaded, or modified

 

Common messages

 

•You cannot delete the profile because it is currently running or is due to run

•%s cannot be modified

•Sorry, the settings cannot be saved: ...

•Unable to import profile '...': ...

•The profile '...' was imported, but it could not be converted to the current version

 

Likely causes and fixes

 

•Profile is running or due to run: wait for the run to finish, or pause the profile first.

•Cannot be modified: the profile is running, or it is owned by another user and you are not in admin mode. Stop the profile or take ownership.

•Settings cannot be saved: disk full, the INI file is read-only, the network store is unavailable (when profiles are stored on a share), or AV is blocking the write. Confirm the profiles folder is writable; move it to a local drive if it is on a flaky share.

•Unable to import or convert: the profile is from a newer or incompatible SyncBackPro version. Use the matching version, or recreate the profile.

 

See Exporting and Importing Profiles and Invalid Profiles.

 

 

19. Installation and update errors

 

Common messages

 

•DeleteFile failed; code 5 Access is denied

•XceedZip.dll is not registered or missing

•OLE Error 800A0183

•Access violation in ntdll.dll

 

First checks

 

•Fully exit SyncBackPro, including the system tray icon. Temporarily disable "start with Windows", reboot, and retry the installer.

•For DLL registration errors, run the installer from an elevated command prompt.

 

 

Looking up Win32 numeric error codes

 

If the log shows a bare numeric error code such as (5), (32), (112), or 0x80070005, these are usually Windows system error codes returned by the underlying API call. The most common codes are listed in section 11.

 

•The canonical reference is the System Error Codes index on Microsoft Learn, which lists every numeric code with its symbolic name and meaning.

•HRESULT values of the form 0x8007xxxx wrap a Win32 code: the low 16 bits xxxx are the underlying Win32 code in hexadecimal. For example, 0x80070005 is Win32 error 5 (ERROR_ACCESS_DENIED).

 

 

What to Collect Before Contacting Support

 

If the steps above do not resolve your error, please collect the following before contacting support:

 

•SyncBack version and edition, e.g. SyncBackPro

•Windows version

•Whether the profile was run manually or by schedule

•Whether SyncBackPro was elevated

•The exact log message and the profile log file

•Source and destination types (local, network, NAS, cloud, FTP, Touch)

•Whether antivirus or endpoint protection is installed

•For cloud problems: the provider, the linked-account status, and whether re-authorisation has been tried

 

The Technical Support Wizard bundles the logs, debug logs, settings, system info, and (optionally) the relevant profile so the support team has the full picture without follow-up.

 

 

When All Else Fails

 

For anything that does not match the above, especially intermittent or "it worked yesterday" failures, enable debug output, reproduce the error once, then generate a Technical Support archive (Help, Tech Support) and send it to 2BrightSparks. See the Help page for support contact options, or visit our online support guide.

 

 

All Content: 2BrightSparks Pte Ltd © 2003-2026