Hello Britgirl,
gnome and x.org is running on that server, the installation is quite similar, the same release, same patchlevel. Now I have deinstalled NoMachine and I have also deleted the /usr/nx folder and then I reinstall it and now it works. I am not sure if have used the right NoMachine version (free one or a demo installation). I will try it again on a different server. Thank you for your help.