What you're seeing here is the triangles that are hidden / not visible in SketchUp. Cleaning up won't help because there is nothing wrong with the objects.
Have you tried applying materials? Does it still show? Maybe it's some exporter setting - I'm guessing you're using cryengine? If so: maybe have a look at
http://www.playuptools.com/downloads/
or this video of someone who exports models from SketchUp to CryEngine.



