What type of lights are you using?

Edit: Here's my last light settings and render settings (Mental Ray). Probably not pro but for the scene I was working on, it seemed to be working pretty well. I used point lights for the interior and I used area lights in the windows. I also used physical sun and sky but I had a daytime scene.

I'm sure you already know that light settings will depend on the scale of your scene. I used 'Cubic' for the Decay Rate on my Point lights but you might want to try Quadratic.