When you exported the map, did you click the screen while the game was sorting through all the files? If so, this can cause crashing issues for some people, me included. If this is what happened then I'd back up all your important files and uninstall/reinstall FH
If that's not the case, then go through your particles folder and make sure that you've deleted every file that ends in _0, _1, etc. I would even go as far to see if your own map's sky/weather/cycle files are causing the problem and to try deleting them (just be sure to save them somewhere!) I hope at least one of these suggestions works out for you