Just look here:
That was the post directly above yours on the forums. In short, problems are common.
If you have a tape drive, do a full backup every night, with recent drives the time this takes is quite comparable to a disk drive, and much faster if the disk is USB1.0 only.
Symantec pushes its "Advanced Disk Backup" but it doesn't assume you have a rotation of USB drives. It's assuming you have an external raid array of disks which provide their own redundancy. What you do then is you backup incrementally onto these devices and then have all those incrementals pulled into one "synthetic" backup on tape. It's a great technology, but you need more than a couple of USB drives to pull it off. If you don't want to use this technology, disks and Veritas are not the combination for you.