Hi,
There seems to be some inconsistency in the Backup Exec database, hence I suggest you to dump this BE database and reload from base.
As a preliminary step we suggest you to update MDAC. You can get the latest MDAC from the following link:
http://www.microsoft.com/data
If this does not help, we suggest you to dump the Backup Exec database and reload it from base.
Follow the steps below:
1) Open BEUTILITY (C:\Program Files\VERITAS\Backup Exec\NT)
2) Add the Media server by Right clicking on "All Media Servers" and choose "Add Media Server"
3) Right click on the media server and stop the services
4) In BEUTILITY Right click on the media server name and choose "Recover Database"
5) Select Drop Database and reload from Base
6) Reboot Server
Note: All media sets, backup-2-disk folder, and other settings will have to be created or configured again, if the option Drop existing database and reload from base is selected.