I am starting to notice a pattern here. If you do a search on GSBC in these forums you will find numerous people are having problems reading DVD's once they've flashed their 451S to that firmware version. I have a December 2003 manufactured 451S that originally came with GSB4 which has worked flawlessly since I bought it over a year ago.
Last week I bumped it up to GSBC and suddenly it went flakey reading discs. It would not recognize several pressed DVD's and various recorded ones. Even the original DVD+RW that came with the drive would no longer mount! The drive would blink for a while, make some clicking and seeking noises, then just stop. Accessing it yielded an error message that no disc is inserted.
I stepped back to GSB4 and it worked perfectly again. Then I went to GSB6, GSB7, and then GSB9. It worked perfectly with each of them. When I loaded GSBA it went flaky again. I loaded the latest 451S@832S code and it also went flaky. Now I'm back to GSB9 and it runs well again.
It seems that a certain batch of 451S drives cannot tolerate firmware newer than GSB9. :sad: