Sorry, your new version has the same error on OS X 10.7.3. I can test 10.5.8 later. Here is the log output:
Mmh, crap. Well, it's not related to Xorg. This error is coming from libssh. I've seen it before (on my server), but it was never fatal.
Please make sure you're running the newest possible version of x2goserver on your remote machine.
Is it possible to start the gui in debugging mode to see more log output?
Unfortunately, there is no other debug mode for x2go. However, I could give you some build with libssh debug support (it will be very noisy though.) There you go: http://www.ionic.de/x2goclient-git-1e13d3578f-2.dmg
This may shed some light on the problem.