Backup Exec has a long history of tape jobs just hanging in mid-run. I have personally experienced this several times with Backup Exec 2012 SP4. Nobody knows why. Specifically, in my experience there's no relation between this problem and defective tapes.
If a tape is bad then you'll usually get some indication of that on the tape drive itself (flashing LED and or message on the display) as well as in Backup Exec (error alert, aborted job). If you got neither then I would just write it down to the as yet unidentified Backup Exec problem, restart Backup Exec services (you'll probably have to kill the Job Engine service via Task Manager - another typical symptom) and retry.
