This error was happening when the preview pane in Windows Explorer was on and a .MSG file was selected. There is no 64-bit handler for .MSG messages in Windows, only 32-bit. So a 64-bit set of handler files needs to be added.
We found this fix at https://www.brandsict.nl/msgpreviewer_en.php:
You need .NET 4.5 or higher. This is native to newer versions of Windows or can be activated via Add/Remove features.
- Download and run this file: MSgPreviewer64_installer. This will create the folder C:\MSGPreviewer64 and place the files there.
- Open an elevated command window and navigate to
C:\Windows\Microsoft.NET\Framework64\v4.0.30319 - Execute these commands:
regasm /tlb C:\MSGPreviewer64\SharpShell.dll
regasm /codebase C:\MSGPreviewer64\msgpreview.dll