What he said. Clean install errors are computer errors, and like he said associated with the Graphics Card. Re-install the LATEST driver software for your comp. Also, make sure that you in fact have not installed any mods. You might have a renegade readme.txt or a mod folder in your directory that will indicate this. If reinstalling driver software doesn't do it, just re-install orbiter. If that STILL doesn't fix it, curse the devil for blighting you so.