Can't use 16x media on 2500a... help

I’m guesing that most media has switched to 16x…never had a problem buring 8x dvd r- media on my 2500a, but I have tried 2 different types (fuji, memorex) and both read as “illegal disks” under nero (alcohol 120 won’t work either). I know I can always buy slower media but I usually get my disks on sale at Circuit City/Best Buy…also, I have already updated with the newest unofficial firmware (didn’t know I could do dl with this burner, neat). Any help would be fabulous.