Hi
I do not know english very well but the one thing I can write is that I also have got Liteon LDW-451S and I upgradet it to 851 with firmware from kowanski (one of users on this forum)
maybe your firmware doesn't recognize properly your dvd disks and that is the problem.
try apply this firmware and you will get 851, but first make backup your eprom and firmware. all needed software to do it you can find here:
www.liteon401s.prv.pl (kowanski's soft)
and don't forget, that is all your risk and is no warrranty it will help you!
but I did it and it goes great!
and something to people from poland:
Chlopaki nie smiejcie sie z mojego anglika, niemiecki znam troche lepiej. Jak ktos umie cos lepiej tu sklecic to piszcie.
best regards