Knoppix v.3.7 install with knx-hdinstall or something like.
I've checked a few sites and from sun's site I've understood that there were a file called /tmp/ICE-unix

here I'll post the suggested sollution of the discussed problem:

When you start KDE for the first time, if you start as root, it creates a /tmp/.ICE unix.
This gives KDE the wrong permissions.
To fix, login in a different desktop and do "chmod 1777 /tmp/.ICE-unix" then a normal user will work.
NOTE: if you login as root in KDE again it'll reset back.