When we login to the server, the X2Go window appears as if the Linux desktop is about to appear and then the session is terminated.
The only thing I see that is noteworthy in /var/log/messages on the server is:
/usr/bin/x2goruncommand: dbus wrapper not available
This error does NOT appear on servers where we are able to connect successfully. However, those servers are running an older version of X2Go server.
This is because starting sessions wrapped in dbus-run-session is a new addition in the latest X2Go Server versions only.
I have not been able to find any explanation for what this error means or how to avoid it.
This is not really an error. I mean, naturally it is, since you will miss functionality (mostly concurrent sessions support for one user if the desktop environment needs a special dbus instance for every session), but starting a session should still work, provided there's not already a DE instance running for the user that tries to start a session. Even then, some DEs are more or less strict on the requirements for parallel sessions - XFCE for instance starts up regardless, while MATE requires a private dbus instance.
Note that RH/EPEL/C7 does not feature the required binary in any package, so on these platforms you'll always get the missing dbus wrapper notification.
We have tried running different window managers like XFCE and GNOME and all produce the same result.
GNOME in RH/EPEL/C7 won't work. XFCE should.
You're actual problem is likely a different one, but I cannot tell what exactly. You probably want to look into ~/.xsession-x2go-*-errors, maybe also enable the debug loglevel in /etc/x2go/x2goserver.conf (no need to restart anything, just spawn a new session) and on the client-side install the debug version of X2Go Client (x2goclient.debug.exe; it's contained in the installer, if you don't have that installed yet, just re-run the installer and make sure to select this option since by default it's not installed automatically) and get a client log via x2goclient.debug.exe > x2goclient-debug.log 2>&1 in a Windows cmd.exe instance (yes, redirection works like that even on Windows).
Mihai