When performing a backup using VSS, a warning is logged in the Application event log of Windows with ID 8230 while taking the VSS snapshot. The backup may subsequently fail.

The warning states:

Volume Shadow Copy Service error: Failed resolving account Administrator with status 1376. Check connection to domain controller and VssAccessControl registry key. Operation: PrepareForSnapshot EventContext: Execution Context: Writer Writer Class Id: {afbab4a2-367d-4d15-a586-71dbb18f8485} Writer Name: Registry Writer Writer Instance ID: {0c8f797c-42cb-410d-a2c3-2877a6c93e38}Error-specific details: Error: NetLocalGroupGetMemebers(Administrator), 0x80070560, The specified local group does   ...

If for some mysterious, unknown reason, your backup suddenly stops working and throws VSS errors, it's usually a good idea to check the following:

If your server is an SBS 2008 or 2011, and have installed updates, you may have to reconfigure Sharepoint:
WSB fails on SBS 2011 after updating Sharepoint (0x800423f0 or 0x800423f3).

If you get errors about VSS failing to create a snapshot, and you have not changed anything on your server recently, it's a good idea to check the presence of a lot of old shadow copies, taking up space. Although old copies will be purged automatically, the VSS Writer doesn't wait around for it, and fails the backup.
So try deleting shadow copies or increase the sh  ...