[ubuntu-it] messaggio di errore

[mauro]

Nessun problema, il sistema funziona bene, ma da un po' di tempo, sul
portatile di casa, quando faccio la verifica nella finestra degli
aggiornamenti software, mi compare questo msg di errore, che non so
interpretare. Tuttavia l'aggiornamento sta funzionando a dovere e non ho
altri problemi (sono su una Ubuntu 6.06 Dapper):

W: GPG error: http://packages.freecontrib.org dapper Release: Le
seguenti firme non sono state verificate perchè la chiave pubblica non è
disponibile: NO_PUBKEY F120156012B83718

quindi compare una finestra con questi msg:

W: Duplicate sources.list entry http://archive.ubuntu.com dapper-backports/main Packages (/var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_dapper-backports_main_binary-i386_Packages)
W: Duplicate sources.list entry http://archive.ubuntu.com dapper-backports/restricted Packages (/var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_dapper-backports_restricted_binary-i386_Packages)
W: Duplicate sources.list entry http://archive.ubuntu.com dapper-backports/universe Packages (/var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_dapper-backports_universe_binary-i386_Packages)
W: Duplicate sources.list entry http://archive.ubuntu.com dapper-backports/multiverse Packages (/var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_dapper-backports_multiverse_binary-i386_Packages)
W: Duplicate sources.list entry http://archive.ubuntu.com dapper-updates/main Packages (/var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_dapper-updates_main_binary-i386_Packages)
W: Duplicate sources.list entry http://archive.ubuntu.com dapper-updates/restricted Packages (/var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_dapper-updates_restricted_binary-i386_Packages)
W: Duplicate sources.list entry http://archive.ubuntu.com dapper-updates/universe Packages (/var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_dapper-updates_universe_binary-i386_Packages)
W: Duplicate sources.list entry http://archive.ubuntu.com dapper-updates/multiverse Packages (/var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_dapper-updates_multiverse_binary-i386_Packages)

qualche esperto?

grazie

mauro