1456 - VSS error in the Windows event log: ConvertStringSidToSid

Symptom

An error presents that starts with "A VSS error occurred in the Windows event log" and contains the function "ConvertStringSidToSid". An example is shown below.

Error: A VSS error occurred in the Windows event log. See FAQ https://bit.ly/2KQA9WI: 'source: 
VSS, level: Error, message: ConvertStringSidToSid(S-1-5-80-3919359670-3540430778-4246408611-
3681914861-206046543.bak)0x80070539, The security ID structure is invalid. Operation: OnIdentify 
event Gathering Writer Data Context: Execution Context: Shadow Copy Optimization Writer Writer 
Class Id: {4dc3bdd4-ab48-4d07-adb0-3bee2926fd7f} Writer Name: Shadow Copy Optimization Writer 
Writer Instance ID: {b85e7187-0689-495e-9347-6d76f2eae01c}' 

Cause

The function ConvertStringSidToSid in the error indicates an issue in the Windows Registry. This usually refers to when Redstor's service tries to backup the Registry via VSS but certain aspects cannot be fixed, as they are unreadable. One of these aspects is user accounts that have been removed and are stuck in SID format. This would mean there is an invalid entry in the following registry subtree: HKey_Local_Machine\Software\Microsoft\Windows NT\CurrentVersion\ProfileList

Solution

To resolve this,

1. Open the Registry Editor (regedit).
2. Expand into the abovementioned subtree and check within it if there is an entry that has a .bak value appended. If so, this may be causing the failure when trying to resolve the SID of the writer.
3. Backup the registry key first, then delete the entry with the extra .bak value.
4. Reboot the machine to check if the issue has been fixed.