Strange

hi
i tried to backup a series so i dont scratch my original . all went ok as reading & writing , but when i play it on my dvd player in my room after a few mins d movie will hang & even will return to main menu . i tought it was my dvd player so i tried on my sisters and same problem . now i tried on my PC dvd player and everything went ok . is it the media im using ? im using ATI dvd-r 16x .