Cannot copy file (2): The system cannot find the file specified.
All versions of SyncBack scan the source then the destination (if necessary). The differences are then found and the files are copied, deleted, or moved. Between the time the scan is done and the time the file is copied, deleted, or moved, there is a possibility that the file has been deleted or moved by another program. This can happen with temporary files, for example.
If the folder is a known temporary folder, e.g. Windows/Temp, then the solution is to exclude the entire folder either using the folder & file selections or by using filters. The other alternative is to filter files of that type or filename. See the help file for details on filtering.