BackupExec failed

Yesterday one of my 18 backup jobs failed. The error was a checksum error on the data being copied to tape. The backup job policy performs a disk-to-disk backup and then runs a duplicate job to tape. The disk-to-disk job completed successfully. The duplicate to tape is the one that failed, which doesn't make sense to me. Why wouldn't the disk-to-disk have a checksum error as well, that has the possibility of the files changing. I'm not sure how the data would change during the duplicate job, the file shouldn't be changing, it's static on the Media Server. I tried the job yesterday, just doing the C drive, that completed fine. I did the Shadow Copy Components (this was the reported checksum error culprit) by itself and that completed successfully. I did both straight to tape and that worked! Crazy. I walked through the Symantec knowledge base article 267554 but that provided no resolution. If the drive or SCSI connection are bad, then the other jobs I ran before and after the failed job should not have worked. If it was drive or file fragmentation, why do the other jobs complete successfully when they perform duplicate jobs. I defragmented the drive just to see if it would resolve the issue, but it didn't. I rebooted the server in question, the Symantec BackupExec media server and even recycled the power on the tape library, no change. This AM the same problem presented itself. I have an open ticket with Symantec through the DirectAssist, but we'll see if they can provide a resolution. Based on my past history with them I'm not inclined to think that they will.