Wait, if you delete an object and add it again the crash is gone? I would guess the wmb is't compiled right. Perhaps an unfortunate combination of models. Or an error in the saved wmp file wich got resolved, when you changed the level.

Why do you bite your teeth into this, if you can resolve the problem. I know you want to know what causes the error. But at this point I would delete and readd a model resave the Level and be happy with it.