Hello Debian-Group! I got one solution for my problem but this ended in one problem that I can't understand!
First: I edited the file in /etc/pam.d which is called kscreensaver and deleted the first line in it, which implies if a user locks a session then any user can log in again in the kde-session only when pressing for example the return button or any other button of the keyboard . This is one idea to avoid the problem of locking the screen because any other user can log in again easily and go out of the session, which locks the screen. The next problem is: When doing this - and I boot the client-station remote(ly) again via DHCP - sometimes you can't write something in the window for log into your kde-user session. Because no button reacts! So I press "restart X-Server" and then everything works fine. The next problem is when locking the client-kde-session (lock the screen) there is no possibility to log in again because the keyboard-buttons (return for example) give no signal! The only possibility to go further is to press strg+alt+backspace, but this can't be the solution I know. What is the problem with this ? On other machines which I booted locally there is no problem with this. I edited also my XF86-Config-4 file but without success! Do you have any idea? Any idea will be appreciated! Really! Greetings Heide