What does "Running NoMachine sessions over a SSH connection is not supported on this server" mean?
When NoMachine client 4 gets message:
Running NoMachine sessions over a SSH connection is not supported
on this server. Do you want to switch your connection to using the NX protocol?
it is likely you are trying to connect by using the SSH protocol and the system login to a server 4.
USE CASE 1: NoMachine client 4 is connecting to NoMachine 4 (free)
NoMachine 4 (free) doesn't support SSH.
You can accept to switch to use the NX protocol or configure the connection in your client later as explained here:
If you need to use SSH protocol with your NoMachine server, you can tunnel the NX protocol into an SSH connection as explained here:
USE CASE 2: NoMachine client 4 is connecting to any of the Terminal Server or Enterprise products
It is likely you you are trying to connect by using the SSH protocol and the system login but support for SSH is disabled on the server.
You can either switch to use the NX protocol (please see USE CASE 1) or enable SSH support on the server:
be sure that SSH is listed in the ClientConnectionMethods key in the server.cfg file (e.g. ClientConnectionMethods NX,SSH,HTTP). Restart the server, even from command line or by Server Status GUI by clicking on 'Stop the server' and then 'Start the server'.