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...