SIRIS, ALTO, and NAS: Datto Windows Agent - Backups Hung at "Preparing Next Volume"



When backups are initiated for a system protected with Datto Windows Agent, the backup status remains on the "Preparing Next Volume" step indefinitely.


  • Datto Windows Agent
  • Datto SIRIS
  • Datto ALTO


The user running the Datto services does not have sufficient permissions to access a required VSS registry key. 


1. Open the Windows Event Viewer of the server that is having issues.

2. Open the Application Event Log.

3. Confirm that this error message is shown:

Source: VSS
Event ID: 8193
Message: Volume Shadow Copy Service error: Unexpected error calling routine RegOpenKeyExW(-2147483646,SYSTEM\CurrentControlSet\Services\VSS\Diag,...). hr = 0x80070005, Access is denied.

4. In the Details pane of Event Viewer, under In Bytes, confirm the name of the user account that generated the error.

vss8193-2.pngFigure 1: Event Viewer

5. From the start menu, open the registry editor by typing regedit. Run the program as Administrator.

6. Navigate to "Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\VSS."

7. Right-click the VSS key and click Permissions.

8. Select the User name found in the error message. You will see that the user does not have "Full Control" of this registry location.

8. In the Allow column,  Check the boxes next to Full Control and Read, then click Apply.

9. On the Datto Web Interface, navigate to the Protect page and start a backup. It should now succeed.

Additional Resources

Was this article helpful?

1 out of 1 found this helpful

You must sign in before voting on this article.

Want to talk about it? Have a feature request?

Head on over to our Datto Community Forum or the Datto Community Online.

For more Business Management resources, see the Datto RMM Online Help and the Autotask PSA Online Help .

Still have questions? Get live help.

Datto Homepage