Hi Marianne ,
You can try below steps to fix this issue,
Step 1 : Check what all media still assigned to this host i.e. media09_bck
bpmedialist -l -h media09_bck
Step 2 : Move any tapes assigned to this host to any working media server ,
bpmedia -mov...
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STS Symantec NetBackup 7.6.1 and NetBackup Appliances 2.6.1