Problem starting X as user

[Frank Wißmann]

Hi all!
Hope there's somebody out there who can help me with the following problem:
When I type "startx" as root all is coming up as expected, the X-Server 
and twm as WM. When I stop it, log in as a normal user and do the same 
there is only a grey screen with a mouse-cursor coming up and doing 
nothing until I kill the X-Server with Ctrl-Alt-Backspace. On the 
original screen from which I tried to start is shown the following error 
message:

AUDIT: Thu Apr 3 20:34:48 2008 836 X: client 1 rejected from localhost 
(uid 1001)
Auth name: XDM-AUTHORIZATION-1 ID: -1
Xlib: connection to "0:0" refused by server
Xlib: Protocol not supported by server

.xinitrc and .xsession both have the same contens "exec startxfce4" and 
the permissions "rwxr-xr-x".

Any thoughts please?

TIA Frank