copied dvd's only play on certain dvd players

i was wondering wether anyone could help me on a simple matter which involves copied dvd's that play on my PC and only play 1/2 or 3/4 of the movie on other dvd players. i don't know if it is the way i am burning the actual dvd or if i am missing a step or another program.

i would be very gratefull if i could get some feedback on this matter

please!!!!!

 

Some DVD players dont play DVD R's - u can check this at http://www.videohelp.com