Backup Problems: "Error: An inconsistency was encountered in the requested backup file."

When backing up a clients SBS2003 SP2 R2 Server we get the following error during the verify process: "Error: An inconsistency was encountered in the requested backup file."
We can read and recover files from the backup, but we have not tried a full restore.

1. The server has two 250 gig and two 500 gig hard drives (two mirrors).  The 250 gig mirror is the OS and Exchange.  The 500 gig mirror is only Data.
2. We backup the system & Exchange with one backup and the data with several other backups due to their size.
3. The backup log file below is for data only and is 95 gig.  The verify fails after 20 gig.
4. The backups go to a 400 gig ATA/100 internal hard drive in workstation in the same building.
5. I have looked at KB928517 and verified that only one backup runs at a time.
6. All the backups fail with the same error almost every time.
7. I have other networks I manage that backup the same way and have no problems, but they don't have anywhere near as much data.
8. The backup command line is: {C:\WINDOWS\system32\ntbackup.exe backup "@C:\Backups\Weekly Full Work Data.bks" /a /d "Weekly Work Data Full" /v:yes /r:no /rs:no /hc:off /m normal /j "Weekly Work Data Full" /l:s /f "\\Shpe74\backups\Weekly Work Data Full.bkf"}
9. We don't get any indications there are any problems with the 400 gig backup drive.
10. The backup log file is:

Backup Status
Operation: Backup
Active backup destination: File
Media name: "Weekly Work Data Full.bkf created 10/27/2007 at 12:00 AM"

Volume shadow copy creation: Attempt 1.
Backup (via shadow copy) of "D: Data"
Backup set #1 on media #1
Backup description: "Weekly Work Data Full"
Media name: "Weekly Work Data Full.bkf created 10/27/2007 at 12:00 AM"

Backup Type: Normal

Backup started on 10/27/2007 at 12:13 AM.
Backup completed on 10/27/2007 at 7:32 AM.
Directories: 22227
Files: 111977
Bytes: 94,730,540,758
Time:  7 hours,  18 minutes, and  50 seconds

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Verify Status
Operation: Verify After Backup
Active backup destination: File
Active backup destination: \\Shpe74\backups\Weekly Work Data Full.bkf

Verify of "D:"
Backup set #1 on media #1
Backup description: "Weekly Work Data Full"
Verify started on 10/27/2007 at 7:32 AM.

Error: An inconsistency was encountered in the requested backup file.
Verify completed on 10/27/2007 at 7:49 AM.
Directories: 2919
Files: 37576
Different: 0
Bytes: 21,509,097,051
Time:  16 minutes and  22 seconds

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