Windows 10 version notes
If the normal version doesn't work, there is a fallback to the windows 10 version of msgpreviewer. This version shows the text as plain text.
How to change the font size
the newest version reads a registry key from: HKLM\software\brandsict\msgpreviewer\fontsize
The value of fontsize determines the size used
In the zip file there is a .reg file you can run to create the registry key.
This is not a valid .net assembly
You might want to check if you are using the 64bit regasm. You might have used the path: C:\Windows\Microsoft.NET\Framework\v4.0.30319
and you should used C:\Windows\Microsoft.NET\Framework64\v4.0.30319 , notice the 64 in the framework directory.
run Command line in administrator mode
Goto the directory: C:\Windows\Microsoft.NET\Framework64\v4.0.30319 , by typing: cd C:\Windows\Microsoft.NET\Framework64\v4.0.30319
type the following commands:
regasm /u d:\MSGPreviewer\SharpShell.dll
regasm /u d:\MSGPreviewer\msgpreview.dll
finally, delete the msgpreviewer directory