Backup job won't start unless scan is run

We are using Back Exec 10d with a tape library. We change tapes each day in all slots. The problem is that when the person who changes the tapes forgets to run a scan after the tapes are changed the backup jobs for that night will not run. The first one queues up and the rest miss their scheduled runtimes since Backup Exec can't find an overwriteable tape.

My question, then, is why doesn't Backup Exec automatically scan for tapes when a job starts? And a followup question, is there a way to run a scan from the command line (since I know you can't schedule a scan from the UI). Then I can create a batch file and run it before the first job.

Thanks in advance.