We're encountering the same problem here.

gnome-control-center

(gnome-control-center:28288): Gdk-WARNING **: The program 'gnome-control-center' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadLength (poly request too large or internal Xlib length erro'.
  (Details: serial 153 error_code 16 request_code 147 minor_code 1)
  (Note to programmers: normally, X errors are reported asynchronously;
   that is, you will receive the error a while after causing it.
   To debug your program, run it with the GDK_SYNCHRONIZE environment
   variable to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error() function.)

lsb_release -a
No LSB modules are available.
Distributor ID: Debian
Description:    Debian GNU/Linux 7.6 (wheezy)
Release:        7.6
Codename:       wheezy

dpkg -l x2go\* nx\* gnome-session-fallback gnome-control-center | grep ^ii
ii  gnome-control-center                  1:3.4.3.1-2                                     amd64        utilities to configure the GNOME desktop
ii  gnome-session-fallback                3.4.2.1-4                                       all          GNOME Session Manager - GNOME fallback session
ii  nxagent                               2:3.5.0.28-0x2go1+git20141113.546+wheezy.main.1 amd64        NX agent
ii  x2goagent                             2:3.5.0.28-0x2go1+git20141113.546+wheezy.main.1 all          X2Go agent
ii  x2goserver                            4.0.1.18-0x2go1+git20141006.949+wheezy.main.1   amd64        X2Go server daemon scripts
ii  x2goserver-extensions                 4.0.1.18-0x2go1+git20141006.949+wheezy.main.1   all          X2Go server daemon scripts (extensions)
ii  x2goserver-fmbindings                 4.0.1.18-0x2go1+git20141006.949+wheezy.main.1   all          Generic (freedesktop-based) file manager bindings for X2Go
ii  x2goserver-pyhoca                     4.0.1.18-0x2go1+git20141006.949+wheezy.main.1   all          X2Go server daemon scripts (add-ons for pyhoca client)
ii  x2goserver-xsession                   4.0.1.18-0x2go1+git20141006.949+wheezy.main.1   all          X2Go server daemon scripts (Xsession runner)

Is there a workaround we could use to be able to launch gnome-control-center while you're working on a fix ?