First, is this the original DVD or a duplicate? Second, what DVD is it? (There may be a known issue.) Third, what operating system do you have? (If you have Windows XP, click here to download a DRM update and see if it fixes the problem.) Finally, have you tried playing it with real DVD-playing software? (That's just a hobby of WMP.)
Give us a shout back.
Whenever I try to play a movie in wmp I get this message:
Windows Media Player cannot play the DVD because a problem occurred with digital copyright protection.