Problem with model in BGE

I am having a problem with using a model I made with the game engine. When I look at it with Blender GLSL Materials enabled it looks fine. When I look at it with Blender Multitexture Materials enabled some of the faces just sort of vanish. :confused: This vanishing also occurs in the game engine. I can’t seem to figure out why this would be happening. Could somebody explain why this is happening please?

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