See Event Log Event ID 521 Backup – Error Code 2155348129.
The reason that there was an SP1 upgrade run on the SP SEARCH Express
-> inconsistent osearch14 VSS Writer
Basically “vssadmin list writers” allowed me to see that “SPSearch4 VSS Writer” was holding everything up with an “inconsistent shadow copy” error, and a few quick Google searches later I was all good.
Hopefully that helps you get to where you need to be.
In case anyone else gets here due to backup failing with SBS 2011 even on a clean install with all patches, the cause is due to the SharePoint server Search service pack1. To resolve run the
“SharePoint 2010 Products Configuration Wizard” after that you should be able to re run vssadmin and see all errors are cleared.
See also here
My issue was caused by SP1 on SharePoint 2010. After I ran the following command (twice), from a command prompt on the SharePoint Server the backups started to work:
Run the SP Configuration Wizard
check again using vssadmin list writers as admin
And you can see that the errors have gone.
If this does not work try stopping the MS SQL server VSS Writer and try again to make a system state backup.