missing walls. (fixed)

Okay I made a building via Blender (Image 01) and I wanted to see what it looked like in T3D so I exported it as a COLLADA and put it into T3D. But for some reason when I look at the model in T3D I can only see the inside wall when outside (image 2) and the outside wall when inside (image 3) and what is really bugging me is when I stand in the wall I can see both of walls (image 4)...
So I ask what am I doing wrong?

image 1 (the building in blender)
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image 2 (standing outside looking in. there should be a wall there)
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Image 3 (standing inside looking out. Once more wall should be there)

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image 4 (standing in the wall)