Cannot play this disc

Question

We've had our Sony DVP-NS575P player for about 2 years now. In that 2 years it has played maybe 5 movies. I recently took it apart and cotton swabbed the lens- and it magically played a movie. The next day we stuck one in and again it said that it "cannot play this disc". Sometimes it will play, sometimes it won't. I'm at my wits end with trying to figure out what's wrong- any suggestions?