Comment 1 for bug 281950

Same problem here. Fresh Remix -> Intrepid upgrade using Adept2 upgrader tool. Try to log in and start KDE from KDM and submit username and password, screen switches briefly to the loader and then goes back to the KDM login.

Dunno if this is useful, found it in the startup feedback screen:

grep: /usr/lib/kde4/etc/kde4/kdm/kdmrc: No such file or directory
Not starting K Display Manager (kdm-kde4); it is not the default display manager

And X feedback from ~/.xsession-errors:

Xsession: X session started for seele at Tue Oct 21 13:35:06 EDT 2008
Setting IM through im-switch for locale=en_US.
Start IM through /etc/X11/xinit/input.d/all_ALL linked to /etc/X11/xinit/xinput.d/default.
/usr/bin/xmodmap: unable to open file '/usr/share/apps/kxkb/ubuntu.xmodmap' for reading
/usr/bin/xmodmap: 1 error encountered, abording.
x-terminal-emulator: Fatal IO error: client killed
konsole (5179) Konsole::SessionManager::~SessionManager: Konsole SessionManager destroyed with sessions still alive