I have had problems with the startup script /etc/init.d/knoppix-hd-autoconfig shutting down the ethernet card then not being able to restart it, this might be what is happening here.

see this post http://www.knoppix.net/forum/viewtopic.php?t=14325

The workaround is to edit knoppix-hd-autoconfig so it doesn't fiddle with eth0.