How about a little bit more info? Or if you can post a burn log from whatever burn engine you're using? Some info to provide: 1. What program is doing the burning? 2. What type of blank media are you using? 3. At what speed are you burning? 4. Are these movies rips or downloads? All in all, a log would be very helpful.
Bravo, I must agree with 7thsinger, you don't give much to work with. All I can say (in addition to 7thsinger's excellent advice )is " watch your dvds on your pc", and that should solve your problem