This is really for Deniska, but I was wondering if the large maps may be crashing because it's trying to load so many smaller PNG tiles.
Maybe you could have it load just the centered tile, and the 8 surrounding tiles (so it loads only a block of 9 tiles at any one time for any loc you're viewing)?
I would assume map size would then not be a problem at all?
Just a suggestion anyway, I don't really know much about how you put it all together.