When I switch over to a mod with the custom games menu my whole bf1942 just goes completely back to the desktop and closes. I know it may make you view the desktop for a few seconds when you switch mods but it actually closes the game in my case. It use to not do this. A month ago I was switching mods no problem. But today, it seems to do this.
check ur eagames/bf1942/mods/watever mod u tried to startup/archives/bf1942/levels and make sure there is only rfa map files in there