I'm seeing what I assume to be a unique issue. I'm using Backup Exec 2012, which is connected to an Scalar i6k Tape Library and 2 Netapp filers via fiber channel SAN. I backup to the drives using NDMP (which works very well and very fast, currently very happy with this setup). The issue I've been seeing is that while my weekend backup jobs are running the NDMP drives will become disabled. Re-enabling the drives makes them work properly again but unless I'm constantly monitoring the drives it's very easy to miss this and have my NDMP backups fail over the weekend and I have to restart them come Monday.
Looking at the error logs, I believe I have it narrowed down to an issue with cleaning. During the weekend the drives will flag that they need a cleaning. It will attempt to load the cleaning media, fail, and then disable the tape drives. I have so far been unable to find a way to disable the automatic cleaning, and a manual cleaning presents this in the error log:
PVLSVR: [11/30/12 13:32:52]  AdammSession::Execute( ADAMM_SESSION_EXECUTE_SESSION_SET_JOB_INFO )
Unfortunately I don't believe this applies to my current situation (although they are eerily similar). All the fixes described though would do nothing to correct the issue that this only seems to occur when a cleaning is attempted, which the fixes would not apply to.
For now I have ejected all cleaning tapes, and will reimport as needed for cleaning jobs to help prevent automatic cleaning of the drives to see if the drives still encounter the same issue over the weekend. This is quite an annoying bug (if it is indeed a bug with backup exec)!