The error "not enough server storage available" is shown after a few days of use
When using SyncBack to synchronize / backup between two different computers, and UNC paths are being used, after a few days you may receive the error message Not enough server storage is available from Windows (or other programs) and a network connection error from SyncBack.
To resolve this: modify your profile, enable Expert mode (via the burger menu or Click For Options button), go to the Network\Advanced page, and change the option Do not disconnect from the network after the profile has run.
The error message can be related to the SMB version on client or server. For additional details, please read the Microsoft article for the SMB version enabled on your Windows.