Comment 8 for bug 352716

My gnome-panel also disappeared on one box where it is run under Openbox on an NXClient, with similar error messages to those above. Running the gdb procedure I get :

gdb gnome-panel
GNU gdb 6.8-debian
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "i486-linux-gnu"...
(gdb) break gdk_x_error
Function "gdk_x_error" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (gdk_x_error) pending.
(gdb) run --sync
Starting program: /usr/bin/gnome-panel --sync
[Thread debugging using libthread_db enabled]
[New Thread 0xb6cdb750 (LWP 4788)]
Xlib: extension "Generic Event Extension" missing on display ":1048.0".
Xlib: extension "Generic Event Extension" missing on display ":1048.0".
Xlib: extension "Generic Event Extension" missing on display ":1048.0".
Xlib: extension "Generic Event Extension" missing on display ":1048.0".
Xlib: extension "Generic Event Extension" missing on display ":1048.0".
[Switching to Thread 0xb6cdb750 (LWP 4788)]

Breakpoint 1, gdk_x_error (display=0x98ab6a0, error=0xbfe4d9a8) at /build/buildd/gtk+2.0-2.16.0/gdk/x11/gdkmain-x11.c:614
614 /build/buildd/gtk+2.0-2.16.0/gdk/x11/gdkmain-x11.c: No such file or directory.
 in /build/buildd/gtk+2.0-2.16.0/gdk/x11/gdkmain-x11.c
(gdb) bt full
#0 gdk_x_error (display=0x98ab6a0, error=0xbfe4d9a8) at /build/buildd/gtk+2.0-2.16.0/gdk/x11/gdkmain-x11.c:614
No locals.
#1 0xb7f4ec95 in ?? () from /usr/lib/libbonoboui-2.so.0
No symbol table info available.
#2 0xb763ddb9 in _XError () from /usr/lib/libX11.so.6
No symbol table info available.
#3 0xb7645d76 in _XReply () from /usr/lib/libX11.so.6
No symbol table info available.
#4 0xb74848cb in ?? () from /usr/lib/libXrandr.so.2
No symbol table info available.
#5 0x080a1fd9 in panel_multiscreen_init () at panel-multiscreen.c:82
 screen = (GdkScreen *) 0x98c6108
 display = (GdkDisplay *) 0x98c3010
 i = 0
#6 0x0806328d in main (argc=2, argv=0xbfe4dcc4) at main.c:81
 context = <value optimized out>
 program = <value optimized out>
 app = <value optimized out>
 new_app = <value optimized out>
 gc = <value optimized out>
 l = <value optimized out>

Hope this helps.