KB 956697 - Windows Server 2008 Hyper-V VSS writer is not used during a backup job because of corrupted or invalid virtual machine configuration files

In Windows Server 2008, "Microsoft Hyper-V VSS Writer" is not listed when you run the vssadmin list writers command.

When you perform a backup of the Hyper-V virtual machines, the following event is logged to the Hyper-V-VMMS event log:

Log Name: Microsoft-Windows-Hyper-V-VMMS-Admin
Source: Microsoft-Windows-Hyper-V-VMMS
Event ID: 10107
Description:
An error occurred while identifying the Hyper-V VSS writer. Check for any corrupt or invalid configuration files and try again.
In this scenario, the backups of the virtual machines may be inconsistent because the Hyper-V VSS writer is not used during the backup job.

This problem occurs because of corrupted or invalid virtual machine configuration files.

You can grab the update from the KB 956697 webpage.