Error: Azure Backup fails Everyday and cannot decipher error message:

Graham  -

This error translates to: VSS failed to add volumes in the snapshot set to take snapshot during prebackup.

I have seen this when someone was backing up different volumes and then one is removed, but more specifically usually dealing with a volume that had been presented as a mount point is removed.

Standard troubleshooting though is good here:

1. Check your scratch location to make sure it has plenty of free space.

2. Make sure that you are on the latest agent version http://aka.ms/azurebackup_agent

3. At the time of the failure, look in system and application event logs for any errors or warnings.  Pay special attention to VSS.

I hope this helps point you in a good direction.

Chris