Thank you for your help. I am able to make it work after changing permissions of the /tmp folder. However, I ran into some other strange problems:
I installed NoMachine on different servers and all of the virtual desktop work fine when users create GNOME virtual desktop session. However, when users select KDE, only 1 server works while the rest failed. It happenend only with some users. All installation of servers are the same configurations. Could you please take a look at the client log to see you could help?
The Linux server is a shared one and all the tools are installed as standard. So when I install NX, I am keeping all default setup. Like I mentioned, my co-workers and I were able to log in and use for a short while then everything stop. How do I check for space required? usages? Should I install NX to a different location so I can get more space?