I think maybe it is your DVD-player that is having the problems. I have never had the problem on DVD's I have bought, but when making copies of movies it can be a bit of a problems. Using different media and burning on one burner can be successful for playback on one DVD-plyer, but not work on another. Then if you switch to another brand of DVDs it might not work anymore, but work on another player.
Try to see if these DVD's work on another player. If they do I would take the player to a dealer and show them your problem if it is a new player, and try to find out if I could upgrade the firmware myself(Starting point) if it is an old player. If it is an old player and it still has problems or you can't figure out how to upgrade the firmware I would start looking for a new player.
Regards
Popol Vuh
