Ground polygon not physical

I try to make a basic ground polygon with only one texture. I made it in Blender, exported in collada (.dae), then in modelconverter x I exported it into .mdl, then with the ground polygon wizard I exported the mdl to bgl. After it, I put it into my airport scenery with texture of course. I can see this gp, but it's not physical. So when I go onto it, it still has that effect, that I have on grass and I can't see the shadow of my airplane. I tried to attach as platform in blender and also in mcx, butit didn't work. I don't what am I doing wrong or what is the problem.