PROBLEM

The Windows Application Event Log inside the guest VM also shows the below Error Event at the time of failure:

Log Name: Application

Source: VSS

Event ID: 8193

Level: Error

Description:

Volume Shadow Copy Service error: Unexpected error calling routine RegOpenKeyExW(-2147483646,SYSTEM\CurrentControlSet\Services\VSS\Diag,…). hr = 0×80070005, Access is denied.

CAUSE

The user does not have appropriate permissions to the Microsoft VSS registry keys.

More details about this issue can be found here: 

https://blogs.technet.microsoft.com/sp/2013/05/29/event-id-8193-volume-shadow-copy-service-error

SOLUTION

1. Go to the the details tab of the above event log entry (Event ID 8193)
   
   
2. Here you can see the information about the User account that generated the error
   
   
3. Take note of the user mentioned after the “- User: Name:” portion
   
   
4. Give that user full permission to the registry key below:

   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\VSS

5. Reboot the VM
   
   
6. Try the backup again and it should be successful