Check the system event logs, to see if you do not have any event IDs 7, 9, 11 or 15. If you have such errors, then most likely it is a hardware issue.

I am having this same issue - however I do not have any event ID 7, 9, 11, or 15's.

The only warning realted to Backup Exec is #213 - license service
Event Type:Warning
Event Source:LicenseService
Event Category:None
Event ID:213
Date:1/16/2007
Time:2:18:17 PM
User:N/A
Computer:BackupOp01
Description:
Replication of license information failed because the License Logging Service on server \\msexch1-m could not be contacted.
Data:
0000: 17 00 02 c0 ...�