I have the same issue. I connect using FX protocol to a Ubuntu 12.04.4 server that ran an older version perfectly fine. I removed the software and /usr/NX as well as local files, and then installed the latest version.
I can connect but it shows <No available sessions on this server> that links to
The server was unable to make the local display available or access to the local display is disabled.
So yeah, the same boat as rwhyte1
Since version 4 won’t work, where do I fetch the older version?