[SOLVED] kdar as root

[kimu]

Hi,
I will to launch kdar as root. I type kdesu kdar in the Konsole and I got:

Xlib: connection to ":0.0" refused by server
Xlib: Invalid MIT-MAGIC-COOKIE-1 key
kdesu: cannot connect to X server :0.0

I'm not an linux expert. Does anyone know what I can do to make kdar start as root?
Thanks

[EDIT]
I had a not better specified problem with kde at the moment. After rebooting everything went right.