"User has opted for target storage from group XXX but device SmartDisk belongs to group '(null)'" (4042530)

Customer was performing a Phase 1 backup to SmartDisk (SD) and Phase 2 to a tape library that used the "Week" Group Label, but the Phase 2 backup was hanging with the following error messages:

1] Warning 2011/11/22 05:00:32 849 Media backup01.travelbox.local No suitable device for job 849 (instance 318) - request held in queue

With sub text:
User has opted for target storage from group 'Week' but device 'SmartDisk - backup01.travelbox.local' belongs to group '(null)'

2] Error 2011/11/22 08:18:19 849 Jobs backup01.travelbox.local Job Status: Duplicate Aborted

Performed a backup straight to SD without labels and completed successfully.
I then ran a backup straight to the tape library without any labels. This job hung with the same error as above.
I checked Media Management and there were enough media i.e. Blank media to deal with the backup, but noticed that there wasn’t a drive added to the tape library.
I checked the Operating System that the tape library and drive could be seen with cat /proc/scsi/scsi and were visible, so the issue wasn't there.

Drive wasn't added to the tape library NetVault Device Management.

We then removed and re-added the tape library, this time with the drive successfully and now the Phase 1 and 2 backup jobs completed successfully.
The problem was that the customer had forgot to add the drive and NetVault was searching for another drive in the backup process. NetVault found SD and tried to use the same media “Week”, but SD doesn’t use labels in the customers setup and therefore failed with the above error.