My Penryn MBP can't play most of the DVDs I create through DVD Studio Pro 4. It thinks all the DVDs are blank or it ejects them. It especially has trouble with DVDs that were created by my other older (Merom) MBP. The Penryn MBP can play some of the DVDs it creates, but not all of them. For example, I burned a DVD yesterday which worked fine yesterday, but when I tried to play it again, it spits it back out. What is wrong?