I Have A Mitsubishi Big Screen DLP. It Has Developed Small Smudge Like Spots On The Top Half Of The Screen. You Dont Notice Them Unless The Background Or Picture Is A Very Light Color Or White. The Screen Is Clean And Damage Free.?

There are two causes I have found by reading around (I have the same issue.  The lower mirror inside the screen may need cleaning (don't clean the big upper mirror) or the light engine is bad and needs replacement.  

I got blue spots last year and they got better after I removed the front screen and cleaned with air.  Soon I will remove the front screen and clean the bottom mirror.