I'm having the same problem, I have the knoppix 5.0.1 dvd beginner hd install, I grew up on dos so linux is backwards to me so I went with that install, though I'm starting to learn some more. Anyway the problem started when I did an apt-get install vlc, I really wanted vlc and I couldn't find it in the new version. It installed a mess of stuff took a half hour, I presume it updated the security or something, vlc worked great, but now my root password doesn't work. I've tried the above mentioned way, sort of lazy like, used the knoppix cd then made a root passwd with that, went to the superuser file manager, made the drive writable and just edited the files through the filemanager with kwrite. All in all it didn't work , still gives me "incorrect password," even with a blank field and it sucks I finally got everything working the way I wanted it to. Anyway any advice would be appreciated.