We have a PC running 64bit Ubuntu 10.04 and KDE 4.
After discovering that VNC does not work well with KDE 4, we installed the FreeNX server. This works with a NoMachine NX client running on Windows XP with no problems.

We needed another linux PC with the same configuration. To save time we cloned the linux hard disk and installed it in another PC with identical hardware. The IP address & hostname were changed because it had to connect to the same network.
This works fine from the console.

When I try to connect to the second machine using NX, it appears to authenticate and connect but I get a black window and cursor. After a few seconds, the NX client terminates and the window is closed. It suggests that the KDE window manager is not working properly. However KDE runs up correctly from the console or when using VNC.

I can connect over SSH from another linux machine.
I tried removing and re-installing the FreeNX server - same problem.
I even tried re-installing the windows NX client.

I wonder if there is a file that was created on the first machine that needs deleting.

Any suggestions?

Brian.

This is what fixed this for me, hope it helps

sudo -i

ssh-keygen -t rsa1 -f ssh_host_key -C '' -N ''
ssh-keygen -t rsa -f ssh_host_rsa_key -C '' -N ''
ssh-keygen -t dsa -f ssh_host_dsa_key -C '' -N ''

chmod 600 ssh_host*key
chmod 644 ssh_host*key.pub

/usr/lib/nx/nxkeygen
dpkg-reconfigure freenx-server (custom keys)

Here is a useful link.

http://helpinlinux.blogspot.com/2011...server-in.html

Try installing xorg fonts also