Error: Storage Dismounted

Hy Experts...

 

i am having a problem, i have a tape library with 24 slots, i already mounted everything, the first tape with the slots 1,2,3,4,5.

 

but when i turn on the backup, it backup 150 GB and show me a error.

 

Diario -- The job failed with the following error: One or more of the databases for this storage group are currently dismounted.  This backup is incomplete.  Make sure that all databases are mounted, and then resubmit the backup job.

 

Anyone can help me??