Event ID: 521 and 8220
The backup operation that started at ‘time-and-date’ has failed because the Volume Shadow Copy Service operation to create a shadow copy of the volumes being backed up failed with following error code ‘2155348129’. Please review the event details for a solution, and then rerun the backup operation once the issue is resolved.
1. Open elevated command promt
> wssadmin list writers
2. If you see this..
State:  Failed
Last error: Inconsistent shadow copy
3. Install hotfix from MS http://support.microsoft.com/kb/2457458