dude that will be why then! ambient lights are the spawn of satan! Change them to directional lights. Bascially ambient lights will just flatten everything out and illuminate everything in the scene whether it's occluded or not. That will almost undoubtley be your problem Do you have shadow casting turned on for these lights? Ambient lights + shadows = major headaches!!
Alan
Technical Director - Framestore
Currently working on: Your Highness
IMDB