I get the error “Encountered Improper Argument” running WM

Windows 10 version 2004 broke existing applications using the MFC framework, including World Machine.

This should eventually get fixed by Microsoft, but we have released Build 3029 to fix this issue in Build 3028. The bugfix release is available to all customers using build 3028.

Newer versions of World Machine (Build 4000+) are unaffected by this issue.