Erro no apt-get update

Boa tarde pessoal,

Quando digito o comando no terminal "apt-get update" o programa faz a atualização, mas alguns repositórios dão erro, Vou postar abaixo meu arquivo source.lst:

#

# deb cdrom:[Debian GNU/Linux 7.6.0 _Wheezy_ - Official amd64 CD Binary-1 20140712-14:11]/ wheezy main

deb cdrom:[Debian GNU/Linux 7.6.0 _Wheezy_ - Official amd64 CD Binary-1 20140712-14:11]/ wheezy main

deb http://ftp.br.debian.org/debian/ wheezy main non-free contrib
deb-src http://ftp.br.debian.org/debian/ wheezy main non-free contrib

deb http://security.debian.org/ wheezy/updates main non-free contrib
deb-src http://security.debian.org/ wheezy/updates main non-free contrib

# wheezy-updates, previously known as 'volatile'
deb http://ftp.br.debian.org/debian/ wheezy-updates main non-free contrib
deb-src http://ftp.br.debian.org/debian/ wheezy-updates main non-free contrib

deb ftp://ftp.us.debian.org/debian/ squeeze main contrib non-free
deb-src ftp://ftp.us.debian.org/debian/ squeeze main contrib non-free

deb ftp://ftp.us.debian.org/debian/ squeeze/updates contrib
deb-src ftp://ftp.us.debian.org/debian/ squeeze/updates contrib

deb http://ftp.br.debian.org/debian-multimedia squeeze main

deb-src http://ftp.br.debian.org/debian-multimedia squeeze main

deb http://www.debian-multimedia.org/ squeeze main

deb-src http://www.debian-multimedia.org squeeze main
deb http://ftp.br.debian.org/debian/ wheezy-proposed-updates non-free contrib main
# GPG Key: sudo apt-get install debian-multimedia-keyring -y

O erro é esse abaixo:

Err ftp://ftp.us.debian.org squeeze/updates/contrib Sources
Impossível obter arquivo, servidor disse 'Failed to open file. ' [IP: 64.50.233.100 21]
Obter:51 ftp://ftp.us.debian.org squeeze/updates/contrib amd64 Packages
Err ftp://ftp.us.debian.org squeeze/updates/contrib amd64 Packages
Impossível obter arquivo, servidor disse 'Failed to open file. ' [IP: 64.50.233.100 21]
Obter:52 ftp://ftp.us.debian.org squeeze/updates/contrib Translation-pt_BR
Ign ftp://ftp.us.debian.org squeeze/updates/contrib Translation-pt_BR
Obter:53 ftp://ftp.us.debian.org squeeze/updates/contrib Translation-pt
Ign ftp://ftp.us.debian.org squeeze/updates/contrib Translation-pt
Obter:54 ftp://ftp.us.debian.org squeeze/updates/contrib Translation-en
Ign ftp://ftp.us.debian.org squeeze/updates/contrib Translation-en
Baixados 570 kB em 1min 5s (8.759 B/s)
W: Erro GPG: http://ftp.br.debian.org squeeze Release: As assinaturas a seguir não puderam ser verificadas devido à chave pública não estar disponível: NO_PUBKEY 07DC563D1F41B907
W: Falhou ao buscar http://www.debian-multimedia.org/dists/squeeze/main/source/Sources 404 Not Found

W: Falhou ao buscar http://www.debian-multimedia.org/dists/squeeze/main/binary-amd64/Packages 404 Not Found

W: Falhou ao buscar ftp://ftp.us.debian.org/debian/dists/squeeze/updates/contrib/source/Sources Impossível obter arquivo, servidor disse 'Failed to open file. ' [IP: 64.50.233.100 21]

W: Falhou ao buscar ftp://ftp.us.debian.org/debian/dists/squeeze/updates/contrib/binary-amd64/Packages Impossível obter arquivo, servidor disse 'Failed to open file. ' [IP: 64.50.233.100 21]

E: Falhou o download de alguns ficheiros de índice. Foram ignorados ou os antigos foram usados em seu lugar.

Pessoal o que está errado no meu arquivo source.lst??

Desde já agradeço.