Clean Tape job fails

I have a single tape standalone tape drive that backup jobs write to on a daily basis. (We are using B. Exec 2012)

Backup jobs complete properly. But 'tape clean' jobs fail with the following error:

"Physical Volume Library Robot not Found. V-79-57344 (0xe0008113)"

So, it is clear that B.Exec sees the tape device to do backups. I just don't see why it says it cannot do 'tape cleans'.