I was experiencing issues when backing up a local directory to a Netware drive. The files would eventually write but after a few attempts and 30 seconds per attempt. The files were not locked by any process and even after I tested with a dummy directory with dummy files I had the same result.
The syntax that I was using was fairly standard and I ruled out a permissions issue as I could create a folder pair in MS SyncToy which was able to copy files without any issue.
My only way around this was to change the retry time from 30 seconds to 1 second by adding the /W:1 switch at the end of the line:
C:\Backup\robocopy.exe c:\test\ g:\test\ /MIR /W:1 >c:\Backup\test.log
I can only assume that this was an NDS related error and the Netware volume didn’t like the way that the Robocopy process was writing to it.