In further grepping, I discovered that the errors I mentioned:
Error: Failure negotiating the session in stage '7'.
Error: Wrong version or invalid session authentication cookie.
are listed in the /client-side/ session logs:
$ cat ~/.x2go/S-hmangala-55-1381535091_stRgnome-terminal_dp24/sessions
Loop: PANIC! The remote NX proxy closed the connection.
Loop: PANIC! Failure negotiating the session in stage '7'.
Loop: PANIC! Wrong version or invalid session authentication cookie.
but those strings are not found in the client, nor in the server-side nxagent shell script so .. where are they coming from..?
This has been noted in other list postings:
Harry Mangalam - Research Computing, OIT, Rm 225 MSTB, UC Irvine
[m/c 2225] / 92697 Google Voice Multiplexer: (949) 478-4487
415 South Circle View Dr, Irvine, CA, 92697 [shipping]
MSTB Lat/Long: (33.642025,-117.844414) (paste into Google Maps)