Avamar: VSS failure (Event ID 8193)

Volume Shadow Copy Service (VSS) backups are failing with the VSS Event ID 8193 generated on the client.

VSS backups fail with the errors: 

avvss Error <8327>: Unable to successfully process [Wo], targets System State/BootableSystemState/ASR (C:)
System State/BootableSystemState/System
System State/BootableSystemState/Registry

The VSS error Event ID 8193 was found on the server with the statement:

Volume Shadow Copy Service error: Unexpected error calling routine ConvertStringSidToSid([S-x].bak).  hr = 0x80070539, The security ID structure is invalid
 
   OnIdentify event
   Gathering Writer Data
 
   Execution Context: Shadow Copy Optimization Writer
   Writer Class Id: {4dc3bdd4-ab48-4d07-adb0-3bee2926fd7f}
   Writer Name: Shadow Copy Optimization Writer
   Writer Instance ID: {8db89871-83d2-4e39-b4fd-34b73f889c10}

Examining the registry (with the Registry Editor tool regedit) found the following entry located at HKLM\Software\Microsoft\Windows NT\CurrentVersion\ProfileList:

The error is due to invalid entries in the registry, where .bak entries are located at HKLM\Software\Microsoft\Windows NT\CurrentVersion\ProfileList.

1. Open the Registry Editor with regedit.
2. Go to HKLM\Software\Microsoft\Windows NT\CurrentVersion\ProfileList.
3. Find the entry that ends with the ".bak"
4. Backup the registry
5. Delete that entry with the ".bak" extension.
6. Reboot the server 

The solution provided in the Microsoft Forum: https://technet.microsoft.com/en-us/library/ee264196%28v=ws.10%29.aspx?f=255&MSPPError=-2147217396 (External Link)

Event ID description: https://social.technet.microsoft.com/Forums/windowsserver/en-US/7b52f7c1-a783-409e-9af3-da64567676df/vss-error-8193 (External Link)