Storage devices keeps going "offline" after finishing a job

I have Backup Exec v14, running on server 2008 R2.  Everytime I run a differential, or a full backup, the job completes successfully.  However, after the backup, my tape drive goes "offline", and all subsequent jobs will fail until I manually enable it again.  The drive is still reachable via windows, just not through backup exec.  Its easy enough to "enable" it, but its not practical to do this every day.  Any help?  thanks in advance!