Reinstalled x2goserver, still no luck. This is logged in the session file on the client:
NXPROXY - Version 3.5.0
Copyright (C) 2001, 2010 NoMachine.
Info: Proxy running in client mode with pid '6152'.
Session: Starting session at 'Thu Mar 28 13:12:52 2013'.
Info: Connecting to remote host 'localhost:30201'.
Info: Connection to remote proxy 'localhost:30201' established.
Loop: PANIC! The remote NX proxy closed the connection.
Error: The remote NX proxy closed the connection.
Loop: PANIC! Failure negotiating the session in stage '7'.
Error: Failure negotiating the session in stage '7'.
Loop: PANIC! Wrong version or invalid session authentication cookie.
Error: Wrong version or invalid session authentication cookie.
Session: Terminating session at 'Thu Mar 28 13:12:52 2013'.
Session: Session terminated at 'Thu Mar 28 13:12:52 2013'.
NXTransDialog: WARNING! Couldn't start '/usr/NX/bin/nxclient'. Error is 2 'No such file or directory'.
Warning: Couldn't start '/usr/NX/bin/nxclient'. Error is 2 'No such file or directory'.
NXTransDialog: WARNING! Trying with path '/usr/NX/bin:/opt/NX/bin:/usr/local/NX/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games'.
Warning: Trying with path '/usr/NX/bin:/opt/NX/bin:/usr/local/NX/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games'.
NXTransDialog: WARNING! Couldn't start 'nxclient'. Error is 2 'No such file or directory'.
Warning: Couldn't start 'nxclient'. Error is 2 'No such file or directory'.
NXTransDialog: WARNING! Trying with path '/usr/NX/bin:/opt/NX/bin:/usr/local/NX/bin:/usr/NX/bin:/opt/NX/bin:/usr/local/NX/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games'.
Warning: Trying with path '/usr/NX/bin:/opt/NX/bin:/usr/local/NX/bin:/usr/NX/bin:/opt/NX/bin:/usr/local/NX/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games'.