Backups to an NDMP VTL on a DR Series Appliance are "Waiting for Media" - Logs indicating that the media cannot be written to because it is "Write Protected"
The cause for this is not known - but the anomaly is that since NetVault is unaware that its not actually a Physical Tape Library, it is curious that it is getting the "write protected" error. Write protected media - as opposed "Media Read Only" which is set by NetVault - cannot be changed.
Media being "write protected" would indicate that a physical tape has a write protect switch enabled on the actual tape. In this case, there is only solution.
Reboot the DR. Verify that the VTL media is no longer showing as "Write Protected"
This should resolve the issue.