OCC layer rendering problem

I creat a maya scene and want to render the OCC layer.  I create the
occlusion layer from the presets.   I find that the scene render
correctly if the scene is open entironment or outdoor, but it isn't
correct if the scene is close entironment. For example, the scene is
inside of pCube as a house.  I have already reversed the normal and
setup two lights  for this pCube, but the rendering  result is the
whole dark image.
How can I solve the problem?


thanks