Please follow the instructions you get in “What to include” (see below), namely:
– NoMachine product and version on local and remote machine (free version, Workstation, etc).
– Whether the problem arises connecting to a physical or a virtual display.
– Remote and local Windows/Mac/Linux version (Windows XP/7/8, OS X 10.x, Ubuntu xyz, Mint x.y, etc.).
– If on Linux, desktop version (GNOME. KDE, whatever) on client and on server.
That error is reported when the client is disconnected before getting past the session negotiation. It is likely a display problem. It would be useful if you could provide a tar of the server logs to the support.