Hmm that is rather strange.
I must admit I have had my map maker crash my FH a lot, and it's rather annoying though with your issue it sounds kind of foreign to me. Have you recently downloaded any meshes or exported a map recently? I know when I export a map at times my FH map maker will crash. That or the mesh files I downloaded tend to have an issue inside of it, and you might have to slowly remove all new meshes, and slowly load them in and test your FH until it crashes again. Once it does you would know that the mesh file you put in may have corrupted your map maker.
Sadly those are the only things I know. A better explanation of what you may have done beforehand might help out more so that you may find a proper solution.