Client log issue for NX

I'm running a NX node on a Ubuntu 7.04. Usually I'd log on to it from a Windows client on Vista x64. Lately the sessions seemed to die after a period of time. Then I noticed sometimes it popped up messages like these:

Found some clues from this page, even it's in a language I don't know (some sort of Nordic?). So I disabled the error logging of X, and doubled the log file size limit to about 8 MB. Hopefully this would give me more lifetime of my sessions.

The NX included by Ubuntu seems to be old (2.x). I wonder maybe it's dropped by the distro?