Hello,
Some questions I would ask are:
1.) Does this happen with any tape?
2.) Does this happen with any backup ? and does the size of the backup matter?
3.) Is your backup server taxed for memory during a backup process ??
4.) Is your tape drive on a scsi controller that is properly terminated and has no other devices sharing the controller. Sometimes when you have 2 devices sharing the same controller time out can occur.
5.) Is your backexec patched right up to date ?
6.) You could also try .Net 3.0 if your out of ideas.
7.) I also found this from another post with the same problem:
"I would suggest upgrading to the latest revision of 11d. You are currently running the first rev (6235). If you want to get the latest rev, just go to fileconnect.symantec.com or backupexec.com and download the latest installer. It will upgrade your current install and you should not have to recreate anything."
I hope some of these things help you find a resolution.