[xubuntu] Error setting screen resolution in VirtualBox

Hi,

Followed the wiki. Get this

david@david-VirtualBox:~$ xrandr -q
Screen 0: minimum 64 x 64, current 800 x 600, maximum 32000 x 32000
VBOX0 connected 800x600+0+0 0mm x 0mm
800x600 60.0*+
640x480 60.0
david@david-VirtualBox:~$ xrandr --newmode "1368x768_60.00" 85.25 1368 1440 1576 1784 768 771 781 798 -hsync +vsync
david@david-VirtualBox:~$ xrandr --addmode VBOX0 1368x768_60.00X Error of failed request: BadMatch (invalid parameter attributes)
Major opcode of failed request: 140 (RANDR)
Minor opcode of failed request: 18 (RRAddOutputMode)
Serial number of failed request: 20
Current serial number in output stream: 21
david@david-VirtualBox:~$ xrandr -q
Screen 0: minimum 64 x 64, current 800 x 600, maximum 32000 x 32000
VBOX0 connected 800x600+0+0 0mm x 0mm
800x600 60.0*+
640x480 60.0
1368x768_60.00 (0x155) 85.2MHz
h: width 1368 start 1440 end 1576 total 1784 skew 0 clock 47.8KHz
v: height 768 start 771 end 781 total 798 clock 59.9Hz

I also found this thread http://ubuntuforums.org/showthread.php?t=1880909 and have installed the virtualbox-guest* packages.

Here is my graphics support
david@david-VirtualBox:~$ sudo lshw -C display
[sudo] password for david:
*-display UNCLAIMED
description: VGA compatible controller
product: VirtualBox Graphics Adapter
vendor: InnoTek Systemberatung GmbH
physical id: 2
bus info: pci@0000:00:02.0
version: 00
width: 32 bits
clock: 33MHz
capabilities: vga_controller bus_master
configuration: latency=0
resources: memory:e0000000-e7ffffff

There is no xorg.conf in /etc/X11 so not sure about the options to add a modeline to that file, as it does not exist.

Ideas?

Thx.

David