This message indicates that Eggplant is not able to connect to the VNC server on the remote machine. Fundamentally the licensing (fixed vs floating) has no impact on connecting to VNC servers. So some other configuration issue is at play.
Have you verified that you are connecting to the correct port for the production server, ie verified that your fixed versions are connecting to the same port as the floating version. VNC runs on 5900 by default but you may have set it to a different port.
Have you also verified that your VNC host and SSH Host entries are identical in both copies of Eggplant? Subtle DNS issues can occur when it first connects to the SSH host and then applies the VNC host name from the perspective of the SSH host.
This error indicates that your SSH login is probably working ok even from the fixed key copies of Eggplant, otherwise you would get an SSH failure. It logs in first and then attempts to establish a connection the server - it’s at this point that your connection is failing.
If this response does not resolve your issue please don’t hesitate to send an email to firstname.lastname@example.org.