Не могу добавить репозиторий NVIDIA apt-get

Я не могу добавить необходимый репозиторий для установки nvidia-graphics-drivers-319. Я не понимаю, почему ключ не доверяют. Смотрите вывод необходимых команд:

root@barry-III:/home/zombie# add-apt-repository ppa:ubuntu-x-swat/x-updates
 Updated versions of X.org drivers, libraries, etc. for Ubuntu.

This PPA is for stable upstream releases of X.org components.  If you're looking for something even more bleeding-edge, please see the xorg-edgers PPA.

While Ubuntu does not "officially/formally" support these packages, if you discover problems when installing these debs please feel free to report bugs to launchpad.  However, please make sure to clearly state that you are running packages from this PPA so we know the fixes need to come here.

If you are upgrading from one release to another with this PPA activated, please install the ppa-purge package and use it to downgrade everything in here beforehand. sudo ppa-purge ppa:ubuntu-x-swat/x-updates will do it.

[Directions for packaging drivers can be seen at https://wiki.ubuntu.com/X/DriverBuilding]
 More info: https://launchpad.net/~ubuntu-x-swat/+archive/x-updates
Press [ENTER] to continue or ctrl-c to cancel adding it

gpg: keyring `/tmp/tmph015_y/secring.gpg' created
gpg: keyring `/tmp/tmph015_y/pubring.gpg' created
gpg: requesting key AF1CDFA9 from hkp server keyserver.ubuntu.com
gpg: /tmp/tmph015_y/trustdb.gpg: trustdb created
gpg: key AF1CDFA9: public key "Launchpad PPA for Ubuntu-X" imported
gpg: no ultimately trusted keys found
gpg: Total number processed: 1
gpg:               imported: 1  (RSA: 1)
OK
root@barry-III:/home/zombie# apt-get install nvidia-graphics-drivers-319
Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package nvidia-graphics-drivers-319
root@barry-III:/home/zombie#