VSS Writers Failed (Status and Reason)

 Source - http://support.mozy.com/articles/en_US/FAQ/How-do-I-identify-the-cause-of-my-VSS-error

Check status

1. Click on Start, then in the Search bar, type cmd.  
2. When cmd appears at the top of the Start menu, right-click on it and select Run As Administrator.
3. Type vssadmin list writers into the command prompt, then press Enter.

Explore Event Logs

VSS errors are typically registered within the Windows' event logs.

Type eventvwr.msc into the open command prompt, then press Enter.

Within the Event Viewer there are two logs in which VSS related errors may be chronicled:  The Application Log and the System Log.  Under Windows Vista and Windows 7 these logs will be under the category Windows Logs, while in Windows XP these logs will be immediately viewable.  VSS errors will appear in the Application Log as entries with a source labeled VSS, and in the System Log they will appear with a source labeled volsnap.  For both logs we suggest sorting by source, then look for any items that match either of those source types.  Document the Event IDs associated with these errors, as Internet searches for those Event IDs will provide a good start for finding a resolution to your issue.

Take another look at the logs; determine whether there are any repeating errors.  There are many other issues that can contribute to VSS errors, and they may be listed under different source headings.  Some common service errors that impact VSS deal with the COM+ services, or the MSDTC.  Issues with the hard drive or filesystem can also cause VSS issues.  In particular, look within the System log for any errors under the source disk, ftdisk or ntfs.  If you see any errors or warnings under those source types, you may need to perform a checkdisk.