The backup of hyper-V guests via the hyper-V agent failed with the error:
Snapshot provider error (0xE0008516):Resources specified for snapshot do not have any valid data on them. Check if files were deleted or renamed.
From the error itself it appears that Backup Exec for Windows Servers Hyper-V Agent was not able to enumerate the backup selections.
And guess how the enumeration occurs? Over the VSS Hyper-V Writer!
So if the Hyper-V Writer is missing one would encounter backup failures similar to above. If the backup selections are browsed the hyper-V agent selections would not be populated.
There is a fix for the issue where the MS VSS Hyper-V Writer simply vanishes for instance after a backup job failure.
Check this out:
An update is available for Windows Server 2008-based computers to address issues with backing up and restoring Hyper-V virtual machines
Excerpt from the above MSKBA:
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.