Hmm. I wonder. Did you flatten the image afterwards? If everything isn't on one layer, my map maker always crashes.
Is this a problem that has only recently happened? I'm unsure if I am correct but I try to avoid making large maps because they require a lot of time for the game to load it up and can just crash because too many assets. This could be why the game is crashing, at least that is what I think.
Make sure you remove alpha channel as that can cause crashing with the map maker. When loading up the map in general though, duplicate particles also cause crashing so be sure to delete any in your particles folder.
You could also try making the map larger in smaller increments instead of doing it all at once? This would require less of a load for the game and possibly make it load faster.
~ Whisper