If it is an older movie, that indicates a problem with the disc. It doesn't have to be a scratch - it could be a substrate problem. Try using a disc scratch remover polymer (they sell the kits for $10 at the local record shop) on the whole disc (or white toothpaste like Aim) and see if that helps. If not, it could be a substrate problem. If the movie plays all the way through, you may need to find a more tolerant drive.
For example, when I replace my ailing Liteon DVD-ROM, I'll be ordering a Liteon combo drive... because the one in my wife's machine reads right through substrate errors, whereas NONE of my other devices so.