Hello, you are right it was the sun causing the problem ... however I don't understand why the sun would do that kind of effect inside a sealed hollow room (the camera is inside the room)?? Also disabling the sun is not the solution e.g if the sealed room had a door, outside scene would not be rendered correctly without the sun.

You can download the project from here (you need to wait for about 1 minute before the download button appears) :-

http://www.gigasize.com/get.php?d=bkgflly222c