Just after booting, while Kubuntu loads its modules and checks all of it, this message appears and the loading work stops.
As a matter of fact the Kubuntu's login screen never comes and it switches automatically on the tty1 in console mode. So I only can use the ttys 1 to 6 in console mode and the tty7 still out of order.
The following procedure to re-install the NVIDIA driver did not work :
Remove the existing nvidia driver :
sudo apt-get purge nvidia-current
Upgrade to the new driver: (follow this link)
sudo add-apt-repository ppa:ubuntu-x-swat/x-updates
sudo apt-get update
sudo apt-get dist-upgrade
sudo apt-get install nvidia-current
Any idea ? Thank you very much for your time.