Moving all your maps, objects etc into another folder (objects in one folder, maps in another etc) in your desktop or something. Then see if your game works from there,
If it does, it's probably something in the folders you removed. If you've downloaded Derek objects or what ever they're called, or she of the new particles that Glave made, then that could be the cause of the problem. Be sure to double check all of the objects and maps etc to make sure you've done everything correctly.
I've had this problem before, so I removed my objects and the problem was solved. It might not work for you, but there's always a chance it might. Good luck getting your game to work!
--Turtlez