Ok,

I did the apt-get update, here's the error that came back:

Hit http://security.debian.org testing/updates/contrib Packages
Hit http://security.debian.org testing/updates/non-free Packages
Fetched 31.0kB in 3s (8866B/s)
Failed to fetch http://ftp.uni-kl.de/debian-local/di...86/Packages.gz 404 Not Found [IP: 10.64.1.100 80]
W: There is no public key available for the following key IDs:
B5D0C804ADB11277
W: GPG error: http://sidux.com sid Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3916C431F80994F6
E: dpkg was interrupted, you must manually run 'dpkg --configure -a' to correct the problem.
root@Knoppix:/KNOPPIX.IMG/home/knoppix#

Can somebody help me?

Marc.