Map2Dif Lightmap Too Big

I was trying to make a map for a game today, then when I wanted to see in-game, I tried a whole bunch to fix up a lot of intersecting things, then when I finish that, it's still breaking. Constructor gives me no errors, but it doesn't spawn in-game. When I tried Map2Dif it gives me an error saying the lightmap is too big, how do I fix this?