The long fought-against problem named ActiveX Error 429 now has an answer! In cooperation with tim marks, who has willingly tested a proposed solution. Those that get this error while running Menu Inventor, please proceed as follows:

1. Download Comdlg32.ocx into the same folder as you have Menu Inventor (C:\Menu Inventor\ by default).
2. Download reg_component.bat into the same folder and run. A message box should inform it has successfully registered Comdlg32.exe...
3. Re-run Menu Inventor. Vòila!