Ola,
Algo errado aí.
Confirmo o citado pelo libonati
Depois de clicar com o direito no icone do Ubuntu ( iniciar ) e selecionar editar menus, encontrei em sistema/administração/autorizações prontinho esperando para ser marcado.
Experimente verificar pelo terminal
polkit-gnome-authorization
Verifique no synaptic se ele está instalado => policykit-gnome 0.9.2-2ubuntu2
se estiver procure ele nas pastas
/.
/usr
/usr/bin
/usr/bin/polkit-gnome-authorization
/usr/lib
/usr/lib/policykit-gnome
/usr/lib/policykit-gnome/polkit-gnome-manager
/usr/share
/usr/share/applications
/usr/share/applications/polkit-gnome-authorization.desktop
/usr/share/dbus-1
/usr/share/dbus-1/services
/usr/share/dbus-1/services/gnome-org.freedesktop.PolicyKit.AuthenticationAgent.service
/usr/share/dbus-1/services/org.gnome.PolicyKit.AuthorizationManager.service
/usr/share/dbus-1/services/org.gnome.PolicyKit.service
/usr/share/doc
/usr/share/doc/policykit-gnome
/usr/share/doc/policykit-gnome/AUTHORS
/usr/share/doc/policykit-gnome/NEWS.gz
/usr/share/doc/policykit-gnome/README
/usr/share/doc/policykit-gnome/TODO
/usr/share/doc/policykit-gnome/changelog.Debian.gz
/usr/share/doc/policykit-gnome/changelog.gz
/usr/share/doc/policykit-gnome/copyright
/usr/share/locale
/usr/share/locale/ar
/usr/share/locale/ar/LC_MESSAGES
/usr/share/locale/ar/LC_MESSAGES/PolicyKit-gnome.mo
/usr/share/locale/ca
/usr/share/locale/ca/LC_MESSAGES
/usr/share/locale/ca/LC_MESSAGES/PolicyKit-gnome.mo
/usr/share/locale/cs
/usr/share/locale/cs/LC_MESSAGES
/usr/share/locale/cs/LC_MESSAGES/PolicyKit-gnome.mo
/usr/share/locale/da
/usr/share/locale/da/LC_MESSAGES
/usr/share/locale/da/LC_MESSAGES/PolicyKit-gnome.mo
/usr/share/locale/de
/usr/share/locale/de/LC_MESSAGES
/usr/share/locale/de/LC_MESSAGES/PolicyKit-gnome.mo
/usr/share/locale/el
/usr/share/locale/el/LC_MESSAGES
/usr/share/locale/el/LC_MESSAGES/PolicyKit-gnome.mo
/usr/share/locale/en_GB
/usr/share/locale/en_GB/LC_MESSAGES
/usr/share/locale/en_GB/LC_MESSAGES/PolicyKit-gnome.mo
/usr/share/locale/es
/usr/share/locale/es/LC_MESSAGES
/usr/share/locale/es/LC_MESSAGES/PolicyKit-gnome.mo
/usr/share/locale/fi
/usr/share/locale/fi/LC_MESSAGES
/usr/share/locale/fi/LC_MESSAGES/PolicyKit-gnome.mo
/usr/share/locale/fr
/usr/share/locale/fr/LC_MESSAGES
/usr/share/locale/fr/LC_MESSAGES/PolicyKit-gnome.mo
/usr/share/locale/he
/usr/share/locale/he/LC_MESSAGES
/usr/share/locale/he/LC_MESSAGES/PolicyKit-gnome.mo
/usr/share/locale/hu
/usr/share/locale/hu/LC_MESSAGES
/usr/share/locale/hu/LC_MESSAGES/PolicyKit-gnome.mo
/usr/share/locale/ja
/usr/share/locale/ja/LC_MESSAGES
/usr/share/locale/ja/LC_MESSAGES/PolicyKit-gnome.mo
/usr/share/locale/pl
/usr/share/locale/pl/LC_MESSAGES
/usr/share/locale/pl/LC_MESSAGES/PolicyKit-gnome.mo
/usr/share/locale/pt
/usr/share/locale/pt/LC_MESSAGES
/usr/share/locale/pt/LC_MESSAGES/PolicyKit-gnome.mo
/usr/share/locale/pt_BR
/usr/share/locale/pt_BR/LC_MESSAGES
/usr/share/locale/pt_BR/LC_MESSAGES/PolicyKit-gnome.mo
/usr/share/locale/ru
/usr/share/locale/ru/LC_MESSAGES
/usr/share/locale/ru/LC_MESSAGES/PolicyKit-gnome.mo
/usr/share/locale/sk
/usr/share/locale/sk/LC_MESSAGES
/usr/share/locale/sk/LC_MESSAGES/PolicyKit-gnome.mo
/usr/share/locale/sv
/usr/share/locale/sv/LC_MESSAGES
/usr/share/locale/sv/LC_MESSAGES/PolicyKit-gnome.mo
/usr/share/locale/zh_CN
/usr/share/locale/zh_CN/LC_MESSAGES
/usr/share/locale/zh_CN/LC_MESSAGES/PolicyKit-gnome.mo
[],s