I hope you are not running into the following problem here:
http://www.opserver.de/ubb7/ubbthreads.php?ubb=showflat&Number=439415#Post439415

Having said that I've had such a problem twice before:
1) One time I was using a function from a new beta (something simple as floor()) but then the publishing process obviously used the old public version which compiled but led to a software exception.
2) A texture in a wmb level of mine was damaged. It was a multiplayer skateboarding game and as a result I was thinking all the time that is was a code/ some other issue, not a texture problem. I found it by removing parts of the level until it stopped crashing.

(This may or may not help you, probably the latter.)