CDE is not properly displayed

Hi,
I'm working with Solaris 10 on a SunFire V240 server. As root, I can login on CDE, but when I try to log in CDE as another user, I just see a black display and the mouse cursor; there's no front panel and when I right-click I see the Workspace Menu with options: Shuffle up, Shuffle Down, Refresh and Restart Workspace Manager.
I tried deleting the $HOME/.dt directory and the $HOME/.dtprofile with no results.
On the $HOME/.dt/errorlog I see Workspace manager: I/O on display:: :0.0
I'm afraid it is also connected with the fact that if I log as root and then I make su - user, I can't write X window commands like xterm or xclock, I get
Xlib: connection to ":0.0"
Xlib: Invalid MIT-MAGIC-COOKIE-1 Key
Error: can't open display: :0.0
Many thanks in advance for your help.