Perhaps something got screwey with the user Knoppix. No matter- just create your own ser like so:

Log in as root and do:

adduser username

Then just put yourself into /etc/group for everything you want to have acces to and also put your new username in /etc/sudoers like so:

<username> ALL=NOPASSWD: ALL

Then you can use sudo without entering a password everytime. You can then get rid of the user Knoppix if you like. AS root:

deluser knoppix