The menu entry "KNOPPIX > Services > Start NX Server" runs the shell script /usr/bin/nxsetup-knoppix as root. There are a couple of errors creating the "nxuser" user, and the script fails. To avoid the errors, before running the script:

1. Start the "portmap" daemon ("/etc/init.d/portmap start")
2. Remove the symlink /etc/gshadow ("rm /etc/gshadow") and copy a writeable "gshadow" to /etc ("cp /KNOPPIX/etc/gshadow /etc").

Now run the script.

(If you set a password for the regular knoppix user, you can log into the NX client on your other computer as "knoppix").