I think this is what you need.
Log Name: Application
Source: Windows Backup
Date: 4/18/2011 11:15:46 AM
Event ID: 4100
Task Category: None
Backup did not complete successfully because a shadow copy could not be created. Free up disk space on the drive that you are backing up by deleting unnecessary files and then try again.
<Provider Name="Windows Backup" />
<TimeCreated SystemTime="2011-04-18T16:15:46.000000000Z" />
<Data>A shadow copy could not be created. Please check "VSS" and "SPP" application event logs for more information. (0x81000019)</Data>
Kinda looks the same as the other post but I am not sure.