Hi,
This issue could occur due to some kind of corruption in the Backup Exec database. Hence suggest you to perform repair of the Backup Exec database.
Follow the steps below to repair the Backup Exec database:
1. Open BEUTILITY (C:\Program Files\VERITAS\Backup Exec\NT)
2. Add the Media server a. Right click on All Media Servers and choose "Add Media Server"
3. Right click on the media server and stop the services .
4. In C:\Program Files\VERITAS\BACKUP Exec\NT\Data copy the BEDB_DAT.MDF
5. In BEUTILITY Right click on the media server name and choose "Repair Database"