i think you may have polarizer or lcd issues...to check the lcds do this check...
what you do is get a piece of card about a5 sized, and hold it about six inches from the lens with a black image being projected, refocus the projector...if you see small bright patches of grids or lines that are brighter than the rest of the image, you may have dead pixels - never had the opportunity to try this on a dlp, but i know it works for lcd
my lp240 did have what you describe a year ago, and that's when i discovered the above test, it seemed to arise from widescreen borders causing "pixel boredom"
you can see shots of sp5000 dead pixels here
http://www.avforums.com/forums/showp...86&postcount=6
anyway, as far as a refund goes, you can argue that the unit is "not fit for purpose" the consumer advice line can assist you in getting a refund...consumer advice line 08454 040506