Scripts using NAS drive, will fail when executed from Task Scheduler

NAS EX2100 Firmware 1.06.127 icw Windows 7.

I have created a backup.bat script which creates a rar-file from files on my C-drive with the archive-bit set.
In this same script, I also copy those files to the WD NAS (using xcopy ot copy command).
When I manually execute the scripts, all goes fine. When I schedule this into the Task Scheduler, it fails however Task Scheduler says: “Operation completed successfully”.
It looks like all commands referring to the WD NAS are failing when using the Task Scheduler.
I also tried in the script to delete and add the network share, but no luck.

Xcopy is better than copy for this task.  I had found other scripts for other devices did not execute from Task Manager.  Likely a Windows issue…

I tried xcopy, copy, executing rar with output file to the NAS. No luck…