Comment 17 for bug 464591

I've had this in Karmic Alpha.. to fix : boot in recovery mode ( on grub it will be the one that says (Recovery Mode))
Choose normal/resume do a(as root):

mv /etc/X11/xorg.conf /etc/xorg.conf.bak

reinstall graphics drivers

you can search for the currently installed nvidia drivers(generic) with(as root) :
dpkg --get-selections | grep nvidia

if you are installing from NVIDIA BLOB either run with -aNo arguments or say no to auto-configure xorg

I think the problem lies in xorg now needs the PCI-ID of the card in the configuration file