[FreeNX-kNX] freenx not working behind nat: "Error: Failure negotiating the session in stage '10'."

[Rod Morison]

Freenx works fine on my local LAN, but when I try to access from the
outside with ssh port forwarding freenx authenticates, but then stalls.
I've tried with (server-side) both the Suse 10.2 distro version (1.5?)
and the freenx tarball release off the nomachine site (2.0). On the
client side I've tried both the nomachine Windows client and the kde knx
client, exact same result.

All works well on the local LAN, without NAT, but from outside the
session quits with a very obscure error message: "Error: Failure
negotiating the session in stage '10'." (obscure==no google hits on
"stage '10'").

Again, I don't get this error on the local LAN, and the ssh port
forwarding is tested and working fine, AND I do have the "Enable SSL
encryption of all traffic" set (and I've even sniffed the client side
packets to make sure no non-port 22 packets are going out.)

Any help is very appreciated. Here's the session file with the error
message, followed by the server log output...

I've downloaded the source from nomachines and found the error line

NXAGENT - Version 2.1.0

Copyright (C) 2001, 2006 NoMachine.
See http://www.nomachine.com/ for more information.

Info: Agent running with pid '7121'.
Session: Starting session at 'Sat Mar 10 01:01:27 2007'.
Info: Proxy running in server mode with pid '7121'.
Info: Waiting for connection from '127.0.0.1' on port '5021'.
Info: Accepted connection from '127.0.0.1' with port '22725'.
Info: Connection with remote proxy established.
Info: Synchronizing local and remote caches.
Error: The remote NX proxy closed the connection.
Error: Failure negotiating the session in stage '10'.

Fatal server error:
Error: Unable to open display
'nx/nx,options=/home/rod/.nx/C-lipatti-1021-22EED2B2B8AA9415D605FB778814FB47/options:1021'.

-------------------------------------------------------------

Mar 10 01:01:23 lipatti sshd[7037]: Accepted keyboard-interactive/pam
for rod from 127.0.0.1 port 21558 ssh2
Mar 10 01:01:24 lipatti NXSERVER 2.1.0-18[7014]: User 'rod' logged in
from '209.179.2.150'. 'NXLogin::set'
Mar 10 01:01:24 lipatti NXSERVER 2.1.0-18[7014]: Selected node
host:localhost with port:22 'main::selectNode'
Mar 10 01:01:24 lipatti NXSERVER 2.1.0-18[7014]: Current selected node:
localhost is in status: running  'main::selectNode'
Mar 10 01:01:25 lipatti sshd[7044]: Accepted publickey for rod from
127.0.0.1 port 21559 ssh2
Mar 10 01:01:28 lipatti NXSERVER 2.1.0-18[7014]: Session
'22EED2B2B8AA9415D605FB778814FB47' started by user 'rod'.
'NXShell::handler_session_start'
Mar 10 01:01:28 lipatti NXNODE 2.1.0-15[7047]: INFO: Using port '1021'
on node 'lipatti' for session 'unix-kde'. 'main:nxnode:5551'
Mar 10 01:01:28 lipatti NXNODE 2.1.0-15[7047]: INFO: Using host from
available host list: '67.101.167.81'. 'main:nxnode:5552'
Mar 10 01:01:28 lipatti NXSERVER 2.1.0-18[7014]: User 'rod' from
'209.179.2.150' logged out. 'NXLogin::reset'
Mar 10 01:01:30 lipatti NXNODE 2.1.0-15[7047]: ERROR: run command:
process: 7121 finished with: 1 'main:nxnode:3607'
Mar 10 01:01:30 lipatti NXNODE 2.1.0-15[7138]: ERROR: Error when
monitoring session: Session has finished but proxy connection was not
closed. 'NXSessionMonitor:NXSessionMonitor.pm:1395'
Mar 10 01:01:31 lipatti NXNODE 2.1.0-15[7138]: INFO: Directory
'/home/rod/.nx/C-lipatti-1021-22EED2B2B8AA9415D605FB778814FB47' renamed
into '/home/rod/.nx/F-C-lipatti-1021-22EED2B2B8AA9415D605FB778814FB47'
for further investigation 'main:nxnode:5722'
Mar 10 01:01:32 lipatti NXNODE 2.1.0-15[7047]: INFO: Session 'unix-kde'
on port '1021' failed. 'main:nxnode:5765'
Mar 10 01:01:38 lipatti NXSERVER 2.1.0-18[7124]: ERROR: NXNodeExec:
Cannot kill nxssh process: No such process 'NXNodeExec::exec'
Mar 10 01:01:38 lipatti NXSERVER 2.1.0-18[7124]: User 'rod' from
'209.179.2.150' logged out. 'NXLogin::reset'