NTBackup error: An inconsistency was encountered in the requested backup file

The backup that I do at night time is failing for the past couple of days and I am getting 8009 and 017 in the log. Recently, I formatted one external usb backup drives and then ran a manual backup successfully. The successful backup log is below under backup success. Last nights backup did fail with the details below under Backup Failure. Before all this, backups was running fine. I have also been installing all the recent updates, so is this problem related to one of this updates? I have got 1.8gb free space that is available on my OS partition, so will that be enough? Also, the usb drive gets some kind of red light and I have to shut it down then?

Event ID 8009 - End Verify of 'C:' 'Failed' Consult the backup report for more detail.
Event ID 8017 - NTBackup error: 'An inconsistency was encountered in the requested backup file.'

Backup Failure:

Verify Status
Operation: Verify After Backup
Active backup destination: File
Active backup destination: F:\Backup Files\Small Business Server Backup (02).bkf

Verify of "C:"
Backup set #1 on media #1
Backup description: "SBS Backup created on 4/7/2007 at 2:30 AM"
Verify started on 4/7/2007 at 3:48 AM.

Error: An inconsistency was encountered in the requested backup file.
Verify completed on 4/7/2007 at 4:10 AM.
Directories: 818
Files: 6750
Different: 0
Bytes: 995,370,254
Time: 22 minutes and 46 seconds

Backup Success:

Verify Status
Operation: Verify After Backup
Active backup destination: File
Active backup destination: F:\Backup Files\Small Business Server Backup (01).bkf

Verify of "C:"
Backup set #1 on media #1
Backup description: "SBS Backup created on 4/6/2007 at 5:00 PM"
Verify started on 4/6/2007 at 6:20 PM.
Verify completed on 4/6/2007 at 6:27 PM.
Directories: 5813
Files: 47624
Different: 0
Bytes: 9,927,931,309
Time: 7 minutes and 0 seconds

Verify of "D:"
Backup set #2 on media #1
Backup description: "SBS Backup created on 4/6/2007 at 5:00 PM"
Verify started on 4/6/2007 at 6:27 PM.
Verify completed on 4/6/2007 at 6:32 PM.
Directories: 2661
Files: 29537
Different: 0
Bytes: 7,015,629,588
Time: 5 minutes and 7 seconds

Verify of "FRANK\Microsoft Information Store\First Storage Group"
Backup set #3 on media #1
Backup description: "SBS Backup created on 4/6/2007 at 5:00 PM"
Verify started on 4/6/2007 at 6:32 PM.
Verify completed on 4/6/2007 at 6:32 PM.
Directories: 4
Files: 0
Different: 0
Bytes: 379,691,822
Time: 15 seconds

Verify of "System State"
Backup set #4 on media #1
Backup description: "SBS Backup created on 4/6/2007 at 5:00 PM"
Verify started on 4/6/2007 at 6:32 PM.
Verify completed on 4/6/2007 at 6:33 PM.
Directories: 318
Files: 2876
Different: 0
Bytes: 639,263,629
Time: 27 seconds