CAD to Max import problem

I'm facing problem while importing DWG file in MAX 2008 64 bit.
1. Some faces appears black or either invisible.
2. i use Vray for rendering. when i activate the GI, there are black patches on surfaces which are due to some hidden faces inside surface.(like inside a plane you are having a small plane of random shape) when i look for those faces in CAD i find nothing, surfaces are simple with no inside patches.

please help me....is there anything that should taken cared while exporting from CAD...or any other ways to rectify such problems.