Veeam Backup Failure after Hyper-V conversion to VMware

Relevant Errors:
 
Failed to prepare guest for hot backup. Error: VSSControl: -2147212529 Backup job failed.
Discovery phase failed.
Cannot add volumes to the snapshot set.
Cannot add a volume to the snapshot set. Volume name: [\\?\Volume{xxxxxxxxxx}\].
Cannot add volume to the set of volumes that should be shadowed.
VSS error: VSS_E_UNEXPECTED_PROVIDER_ERROR. Code:0x8004230f



This occurs when Guest Processing File System Indexing is enabled on the backup.

The fix for us was that the Hyper-V VSS provider was still installed. To remove this, all you need to do is:

1. Open Regedit
2. Browse to Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\VSS\Providers\
3.  Find {74600e39-7dc5-4567-a03b-f091d6c7b092} (If you expand it, the default value is "Hyper-V IC Software Shadow Copy Provider")
4. Delete the entirety of the {74600e39-7dc5-4567-a03b-f091d6c7b092} key (NOT the VSS or Providers keys)
5. Reboot

Run the backup again, and this time it should complete. If not, or if that key doesn't exist, then you have an unrelated VSS issue and you can get further info from command prompt with the following command:
vssadmin list  writers