As a matter of fact, it is a mirror overload.
I just changed the mirror address to free.fr, and it worked just fine.
(to change the mirror in french ubuntu version, gnome desktop, go to "système"->"Administration"->"Logiciels Ubuntu"->"Télécharger depuis : Autre...", and select another mirror).
This bug is SOLVED
As a matter of fact, it is a mirror overload.
I just changed the mirror address to free.fr, and it worked just fine.
(to change the mirror in french ubuntu version, gnome desktop, go to "système" ->"Administrati on"->"Logiciels Ubuntu" ->"Télécharger depuis : Autre...", and select another mirror).
This bug is SOLVED