If you're sure the DVD has burnt as a movie and not as a series of pictures (which not all DVD players support) then its probably due to the DVD-R being incompatible with the player. This shows in various ways...
1. Plays without problems (compatible)
2. Plays mostly but pauses now and then at random places (slightly incompatible)
3. Plays but pauses at a lot of random places (very incompatible)
4. Doesn't even get recognised as a DVD (incompatible)
Many think that a DVD is a DVD just like a video tape is a video tape but they're not. The best DVD players are actually the really cheap and cheerful ones. I've found they play the largest range of formats where the more expensive ones are often limited. I bought mine (ALBA) for £60 from Argos about 5 years ago and its multi-region, plays PAL and NTSC (those from America) including MP3, VCD and SVCD. Just doesn't like picture discs or DivX movies.
When buying blank media or even thinking of buying a new DVD player/burner check out
www.videohelp.com and check out all the reviews there. You can cross reference players/burners with different types of media and using feedback from others can see what will and won't play.