Hello Again...
I have a case interesting to study and resolve.
By mistake i have some Hyper-V servers with automatic windows updates and restart at 3:00 am by default, those servers are integrated in several backup job that run at that hour (3:00 AM).
When the windows update occurs, of course the Backup job Fail, because the server restarted while the backup job is runnnig.
Check that the server that restart is the Virtual, not the Phisical where the backup exec is installed.
What happen later? a very fast Backup job become in a Very Slow Bakcup Job.
Now i Know that if a Hyper-V server restart while a bakcup job is backing it, the next Backup Job is very Slow.
This happen to me in several servers, with diferents Hyper-V servers, with diferent Backup job
i open another topic for the same problem, you can see this https://www-secure.symantec.com/connect/forums/exchange-mailbox-backup-job-very-slow-three-weeks-ago
it was the same problem in a diferent server, i open a case by telephone and the tech support don´t help me with this, they don´t know how to resolve this problem.
In the picture you can see that the job was very fast, over 4000MB\min, on 13/9/2012 the jod FAIL because the virtual server restart during the backup job, and now 14/09 the job was very Slow 659 MB\min
The Only solutios for me in this cases was Uninstall and Reinstall the Backup exec 2010.
For god should be another solution less radical, i understand that maybe a file was corrupt, but there isn´t any solutions for this apart Uninstall-Reinstall.
I hope if somebody with some light with this issue.