You do not appear to be using the NVIDIA X driver on Linux Ubuntu

After a regular upgrade on Linux Ubuntu Lucid 9.10, I was greeted with the following message:

You do not appear to be using the NVIDIA X driver. Please edit your X configuration file (just run `nvidia-xconfig` as root), and restart the X server.

I tried many forums to return this to normal. They seemed all too complicated and didn't solve the problem, more importantly.

Finally, I solved it by running a combination of commands from two different forums:

To use NVIDIA-provided driver, you will need to remove Nouveau first. You can remove it from a command-line by entering this:
sudo apt-get --purge remove xserver-xorg-video-nouveau
(from this ubuntu forum )

1) Make sure that the kernel headers for your kernel are installed
sudo apt-get install linux-headers-$(uname -r)
2) Install the nvidia driver:
sudo apt-get install nvidia-current (or nvidia-173 or nvidia-96,
depending on your card)
3) Select the driver that you wish to use (you can install all of the
nvidia drivers but use only at the time):
sudo update-alternatives --config gl_conf
sudo ldconfig
sudo update-initramfs -u
4) Configure your xorg.conf
sudo nvidia-xconfig
5) Restart your computer (restarting only the xserver might not work)

(from this launchpad forum )

Hope this helps