dual monitor ubuntu issue

I’ve recently added to my computer a graphic card I was given in order to have the ability to use a second screen. I think the card is recognised because if I go to System->Administration-> Nvidia X server Settings (with ubuntu 10.04), it shows GPU-0 and GPU-1. The first one is probably the integrated gpu I had been using until now.
This card uses a DMS-59 connector, and I have a DMS-59/2*VGA adapter.

My problem is that the Nvidia X server setting window only finds one display, which it names X screen 0.

When I go to system->preferences->monitor, it says “It appears that your graphics driver does not support the necessary extensions to use this tool. Do you want to use your graphics driver vendor’s tool instead?”. If I click yes, it brings me to the Nvidia xserver settings window, and if I click no, it also says only one monitor is found (even if I click ‘detect’).

I double checked that every cable is correctly connected, so I don’t understand why ubuntu can’t find the second monitor.

I tried the tutorial on this website : http://myprogrammingblog.com/2011/09…ia-video-card/
But at one point I don’t get the same output: sudo nvidia-xconfig returns:

Using X configuration file: “/etc/X11/xorg.conf”.

VALIDATION ERROR: Data incomplete in file /etc/X11/xorg.conf.
Undefined Device “(null)” referenced by Screen “Default Screen”.

Backed up file ‘/etc/X11/xorg.conf’ as ‘/etc/X11/xorg.conf.backup’ New
X configuration file written to ‘/etc/X11/xorg.conf’

What could I do to be able to use my second screen, or else make sure what component is faulty and needs to be changed ?

Thanks.