I believe this is when the panes of the navigators have been collapsed so far that all you see is a grey bar at the bottom of the navigator. If you hover over and select that gray line the panes will be restored. I don't think you have to go to the trouble of editing the registry:
Unfortunately I can't answer your questions on the license, but could it be that you only have a limited number of classification licenses, and that's why it works for some users and not others?
Today i've found the reason of this issue - it's license. Unfortunately in my case nx_access_tcclass license and classification_access license needed. I edit NX run script to connect to other license server, where classification_user license type exist, and issue went away.
Thanks all for your attention.