Sorry for the vague description of the problem.
Exactly:
-I have an application server (because some applications are installed only on that server), a file server and some PCs.
-The application server exports by NIS (ypserv) usernames and passwords in the network and the file server shares by NFS a directory with users home files.
-On every station in the network I have a NIS client (ypbind) and I mount the directory shared by the file server in the local /home directory. Also, on every station I use X11 with gdm for login.
-In the gdm login window, if I choose whatever display manager (gnome, wmaker, etc.), excepting kde, everything works well.
-In the gdm login window, if I choose KDE, after login ksplash runs a quite long time and after that I have nothing on the screen, except the background image, and I can do nothing with the computer.
-The .xsession-errors files is:
/etc/X11/gdm/PreSession/Default: Registering your session with wtmp and utmp
/etc/X11/gdm/PreSession/Default: running: /usr/X11R6/bin/sessreg -a -w /var/log/wtmp -u /var/run/utmp -x "/var/lib/gdm/:0.Xservers" -h "" -l ":0" "student"
/etc/X11/gdm/Xsession: Beginning session setup...
/etc/X11/gdm/Xsession: Setup done, will execute: /usr/bin/ssh-agent -- /etc/X11/xdm/Xsession KDE
startkde: Starting up...
ksplash: WARNING: KGenericFactory: instance requested but no instance name or about data passed to the constructor!
kbuildsycoca running...
DCOP Cleaning up dead connections.