Model problems

I've been having a problem with the stability of the Torque Engine when I use my lightwave models. When I use the Orc model the game runs fine. When I switch it for my model sometimes everything works fine, sometimes only the player character loads, the other npcs load as well but you can't see them unless you're in the design mode and sometimes the game will crash and burn when you try to load the level.

I'm not sure if there is a coding error or if there's problems with the model itself or with the way it's being exported. Does anyone have any advice or know where I should start looking for the problem?