All licensed slots on Library are full and the drive(s) have tapes in them.
For every one drive in the library that has a tape, there needs to be at least one slot that is empty (i.e. if there are two tape drives with tapes in them, there needs to be two empty slots).
1. Pull the needed amount of tapes from the library,
2. Log into the web interface for the Library and move the tape(s) from the drive(s) to an empty slot
3. In Backup Exec, right-click the slots and perform a scan and wait for the drive(s) to show as empty