With a lot of the models I have been importing from a game there are dark spots in some places. I removed doubles already and recalculated normals, but I still get this when rendering:
The dark spots are on the top and bottom walls on the right side. It's not a shadow because moving the sun lamp and even using ambient occlusion does nothing. I checked the normals, but they look fine.
The only things I can thing of that make this (imported) object different from one made from scratch are that it is already triangulated since it is a game asset, and it has sharps, which I have been told can store data. I'm probably missing something here; I've never seen this before though.