|Thanks for your input Derek.|
The DVD is absolutely spotless (as are others in this set of five for the third season of the show). Just to be safe, I already took the DVD player apart and cleaned it (although it was pretty clean, and I used an alcohol swab to clean the "lens"), and it made no difference.
I'm pretty sure the DVDs are copy-protected, but I will check when I get some free time.
Any other helpful thoughts, anyone???