Altaro VM Backup Support Centre

Backup Failed due to a Microsoft Shadow Copy error caused by an "Access Denied" error on the VSS Registry Key in the Guest VM

Last Updated: May 30, 2016 03:44PM CEST


  1. Altaro VM Backup reports a Backup failure due to a Microsoft Shadow Copy error indicating a VSS failure within the Guest, as below:

    The operation encountered an error. (Error code 'BASEBACKUPCONTROLLER_016')
    Additional information is available:
    Hyper-V reported that there was a problem taking an internal shadow copy on this VM. This may be a temporary problem and the Microsoft recommended way to fix this error is to wait ten minutes and then repeat the operation, up to three times. (Error code 'VSS_4104')

  2. 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
    Volume Shadow Copy Service error: Unexpected error calling routine RegOpenKeyExW(-2147483646,SYSTEM\CurrentControlSet\Services\VSS\Diag,…). hr = 0×80070005, Access is denied.



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

More details about this issue can be found here:



  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


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