A Windows 11 update might stop Outlook or other Office apps from working because of a conflict with anti-virus software.
The trouble started with KB5027231 a Windows 11 update released 13 June 2023 which, among other things, fixed a file copying bug.
15 days later Microsoft admitted there was a bug in the bug patch. Not the first time that a Microsoft ‘fix’ has caused yet more trouble.
This time Outlook, Office apps and other unnamed ‘third party’ apps could not start because the Windows update conflicted with some anti-virus products.
The problem only applies to 32-bit apps on 64-bit Windows 11 with certain anti-virus software.
Checking the Windows Event Log, there’s an access violation with the error “module is unknown”. But most people don’t know about the Event Log, all they know is the program won’t start.
Microsoft named “Trellix Endpoint Security version earlier than 35.31.25” as a known conflict however there’s a hint that other AV software could have the same problem.
The fix is to update anti-virus software. The latest Trellix product fixes the problem and presumably any other AV makers have released similar patches.
Meantime customers are left with some all too familiar questions. Why didn’t Microsoft’s supposedly extensive testing pick this up before release? This is hardly the first time there’s been a conflict with a major anti-virus product. Why did it take Microsoft over a fortnight to admit there was a problem? Consider all the time and money Microsoft customers wasted on the bug during that time.
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