Problem with faces in BGE

This is just weird problem I tried to fix but nothing works…

Well, I’m creating some FPS game. Map is made with other software, exported as .obj and then imported into blender. Everything looks normal until I start BGE. Faces looks like a flat. When I try to press “Smooth” it doesn’t help. Just check out the pic and you understand what I mean.
I’m wondering what causes this problem and how to fix it. It looks like this also when I set viewport shading to solid.

Thank you for your help.


maybe a “double vertexes” problem ( I guess not)?
Enter “Edit Mode”, select all vertices, and press the “Remove Doubles” button…who knows?