If you are backing up your Hyper-V virtual machines using our VSS writer (backing up the physical server) you should be aware of a new Hotfix (KB959962) we released today that addresses three issues.
If you back up a Hyper-V virtual machine that has multiple volumes, the backup may fail. If you check the VMMS event log after the backup failure occurs, the following event is logged:
Log Name: Microsoft-Windows-Hyper-V-VMMS-Admin
Event ID: 10104
Failed to revert to VSS snapshot on one or more virtual hard disks of the virtual machine '%1'. (Virtual machine ID %2)
The Microsoft Hyper-V VSS Writer may enter an unstable state if a backup of the Hyper-V virtual machine fails. If you run the vssadmin list writers command, the Microsoft Hyper-V VSS Writer is not listed. To return the Microsoft Hyper-V VSS Writer to a stable state, the Hyper-V Virtual Machine Management service must be restarted.
You cannot restore a Hyper-V virtual machine if the virtual machine was configured to use a legacy network adapter.
You can review the KB article and download the fix at http://support.microsoft.com/default.aspx?scid=kb;EN-US;959962.
Hyper-V Integration Test Lead