Cannot copy file (2): The system cannot find the file specified.
All versions of SyncBack scan the source, then the destination (if appropriate). The reported results are compared, the differences are calculated and, if applicable, presented for review & confirmation. The process of copying, moving or deleting then commences. Between the time the scan & comparison (and review, if any) are completed and the copy, delete or move is attempted for a particular file, there is a possibility that the file in question has been deleted, renamed 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 by an appropriate mask. See the Help file for details on filtering.
Recent versions of SyncBackSE/Pro also have an option on the Log settings page to record these errors as a Warning (instead of a critical Error). Warnings do not (by themselves) set the overall Result of the profile run as a Failure (thus, you may not know they are there unless you check the log). Careful consideration should be given to the fact that using this option is telling SyncBackSE/Pro to treat an error as 'not an error'. The files in question right now may be 'obvious' temporary files, but using this option will also semi-suppress notification of future issues (if any) with files that cannot be read because of more serious problems (for example, disk errors, file corruption, etc). Use at your own risk. This option is not available in SyncBackFree.