Did you ever get this code while using FreeFileSync: “Windows Error Code 1314: A required privilege is not held by the client.“?
I did. Many times. I thought it was a Linux file permission error on my Raspberry Pi 3 OMV setup, and I chmodded and chowned an unbelievable amount of times, to no effect. And then, while setting up a new temporary NAS on a Raspberry Pi 3, I found a new page: “Windows Error Code 1314: A required privilege is not held by the client.”
If you don't really need to copy file system permissions, turn them off in global settings.
I solved the problem!