Unit is a Sony DVP-NS715P, ser no 2026425 2b, that only plays some
DVD's. The girl I'm looking at it for said it only plays one disk,
but I could only get it to not play one of my disks, and it played all
others normally. I know the DVD it doesn't play is good, the player's
lens is completely clean, I cleaned it with good isopropyl just to be
sure, still the same thing. It searches the disk for a while, and
then says the disk cannot be played. Any idea what sort of problem
this is? All help appreciated, as always.

Steve