Had a customer whose ntbackups suddenly stopped working on Small Business 2003. On further investigation ntbackup was trying to write the backup to the miniqic type of tape drive yet the actual tape that was in the drive was the travan tape (bearing in mind these tapes have been in use for a long period of time). Apparently there is a known problem with NTBackup incorrectly choosing the backup tape type on a drive that supports multiple tape types (KB article 831664).
When a backup starts, it immediately fails with the error “The requested media failed to mount. The operation was aborted”, even if the tape is in the tape drive. Some tape drives support tapes with different block sizes. Windows Small Business Server 2003 backup chooses the first tape type available, which may not correspond to the tape type of the tape in the drive.
This problem is most commonly seen with the Travan 20 tape drive. Windows Small Business Server 2003 backup chooses the MiniQIC tape type instead of the Travan Tape type.

Applying the hotfix makes it work (and it didnt need a reboot). I’m mystified as to why its suddenly started doing this – I did apply another tape related hotfix about a week and a half ago but backups have run correctly since then. Very strange.