You may find that there are errors in the profile's log that state (as the reason for copy failure to the side quoted):
This operation is supported only when you are connected to the server (1251) (note: the number and text may be in the reverse order in some cases)
We have in the past traced this rather misleading message (it may be a mis-translation by Windows locally of the actual signal from the device) to an inability to support our Safe Copy process.
You can try turning off the Safe Copy function via:
Modify profile > Expert mode > Copy/Delete > Advanced > 'Make safe copies...'
If the networked device is a Windows device (another server or PC), it is possible the underlying problem is privilege/permission-based, as there should be no actual functionality restriction in a Windows system in performing the 'rename over the top' operation involved in Safe Copy, but we cannot offer bespoke support solving the rights issues involved if so. If the device is a NAS device, or some other OS is involved, it may be a simple restriction in functionality. Unfortunately, there is no way to tell from the error message which is the case.
It is possible some other uncommon Windows error messages such as:
A required privilege is not held by the client (1314)
can be also cured by switching off Safe Copy. This example obviously does tend to suggest the underlying problem may be rights-based, which may be solvable by re-configuring the device or the account in use.
This example (and similar messages) may also arise because of an optional setting in SyncBack to try to copy or set various extra info, such as copying folder\file security, file creation dates, force-setting LastModified stamps, and so on. If in doubt, try a basic profile - with Safe Copy switched off - and no other non-default settings. If it works then, try adding the previous extra settings back one at a time until the error re-occurs, at which point you have likely found the incompatible setting.
Please bear in mind these are Windows error messages - our software is simply quoting them for your information.
Applies to: SyncBackPro/SyncBackSE/SyncBackLite/SyncBackFree
(Note: SyncBackLite/Free does not support copying folder\file security, or setting file creation dates, or certain other 'extra' settings. However, Safe Copy is supported.)