Hello z,
Does backup job fail immediately or does it fail after backing up some data.. Are you backing up data to hp library...if yes than check for hp services like hp insight, proliant, management home page if this services are running stop all this services and restart backup exec services nd try a backup with NEW JOB...
1)Another thing which can be checked is firmware update the tape drive and medium changer firmware to the latest one
2)Update scsi card drivers to which library is connected to the latest one...
3) please go through the event viewer before performing above steps to make sure there are no events like 7, 9, 11 or 15....if found any contact hardware vendor to get hardware fixed...
Hope this resolves your issue....please mark this as solution if this helps...