Backup Error_reverting to non-shadow copy

Shadow Copy Backup scheduled to backup My Documents.

Why do I get this message?

Error returned while creating the volume shadow copy:800423f3
Reverting to non-shadow copy backup mode.
Backup of "C: "
Backup set #1 on media #1
Backup description: "Set created 10/7/2006 at 11:45 AM"
Media name: "System Backup.bkf created 10/7/2006 at 11:45 AM

Backup Type: Normal

Backup started on 10/7/2006 at 11:46 AM.
Warning: Unable to open "C:\Documents and Settings\Onemac\Local
Settings\Application Data\Microsoft\Windows Live
" - skipped.
Reason: The process cannot access the file because it is being used by
another process.


Warning: Unable to open "C:\Documents and Settings\Onemac\Local
Settings\Application Data\Microsoft\Windows Live
" - skipped.
Reason: The process cannot access the file because it is being used by
another process.


Warning: Unable to open "C:\Documents and Settings\Onemac\Local
Settings\Temp\~DFC3E1.tmp" - skipped.
Reason: The process cannot access the file because it is being used by
another process.


Warning: Unable to open "C:\Documents and Settings\Onemac\Local
Settings\Temp\~DFC3ED.tmp" - skipped.
Reason: The process cannot access the file because it is being used by
another process.


Warning: Unable to open "C:\Documents and Settings\Onemac\Local
Settings\Temp\~DFCACB.tmp" - skipped.
Reason: The process cannot access the file because it is being used by
another process.


Warning: Unable to open "C:\Documents and Settings\Onemac\Local
Settings\Temp\~DFCADE.tmp" - skipped.
Reason: The process cannot access the file because it is being used by
another process.


Backup completed on 10/7/2006 at 11:46 AM.
Directories: 263
Files: 954
Bytes: 91,733,413
Time: 33 second

WinXP SP2
No Server 2003!!!
Event Log: Started@Automatic
System Restore Service: Started@Automatic
Volume Shadow Copy: Started@Manual

VSS Error 5013 logged in event viewer.