If the files played fine from hard drive, but not from the disk, the media (and or its compatibility with your drive) is the most likely cause. Even if the burn didn't fail, it may have too high of errors to read fast enough to play video. If you are trying to read data, the drive can slow down to read if there are issues. If you are trying to read data to play video, and it has to slow down too much, the player might not like that. One way to test would be to copy the data back off the disk to the hard drive, and see if it plays the copied files from the hard drive then. That will test if the video got corrupted somehow and or if the disk is even readable (but maybe not readable fast enough to play video).
Doing an error scan with cdspeed would reveal more.
easterbunny gave some other recommendations of things to look at, but thats what I would try first.