PacMan777, I couldn't agree with you more! Wise consumers will look into the issue before they buy. The rest will just be puzzled why the disks don't play on their old reader. Even if they post their problem on this forum they will be lucky to find out why. The issue is both arcane and obscure. There are plenty of reasons a disk will not play on an old drive the booktype is only one of many possible reasons. I had completely forgotten about the flag. Once it is set in the firmware one tends to forget that the flag is set. As arcane as it is, I set my booktype flag right away. I feel fortunate that I read this thread to remind me about a flag I had forgotten.
I wouldn't consider it arcane, just a matter of covering as many bases as possible. Players that read only DVD ROM are still being manufactured. The one I mentioned was a promo unit an acquaintance received as a gift. With DL recording, a lot of people noted improved reading of the recorded media when booktyped to DVD ROM.
