Related error message
debian:/# apt-get update Ign http://security.debian.org lenny/updates Release.gpg Ign http://security.debian.org lenny/updates Release Ign http://security.debian.org lenny/updates/main Packages/DiffIndex Ign http://security.debian.org lenny/updates/main Packages Ign http://security.debian.org lenny/updates/main Packages Err http://security.debian.org lenny/updates/main Packages 404 Not Found [IP: 195.20.242.89 80] Ign http://ftp.uk.debian.org lenny Release.gpg Ign http://ftp.uk.debian.org lenny Release Ign http://ftp.uk.debian.org lenny/main Packages/DiffIndex Ign http://ftp.uk.debian.org lenny/main Packages Ign http://ftp.uk.debian.org lenny/main Packages Err http://ftp.uk.debian.org lenny/main Packages 404 Not Found [IP: 83.142.228.128 80] W: Failed to fetch http://security.debian.org/dists/lenny/updates/main/binary-armel/Packages 404 Not Found [IP: 195.20.242.89 80] W: Failed to fetch http://ftp.uk.debian.org/debian/dists/lenny/main/binary-armel/Packages 404 Not Found [IP: 83.142.228.128 80] E: Some index files failed to download, they have been ignored, or old ones used instead.
Solution
Debian support for Lenny distribution ended in 2012. There are two solutions for this problem.
First, you can select a mirror still supporting Lenny. In order to do so, exchange the content of /etc/apt/sources.list by:
deb http://ftp.de.debian.org/debian-archive/debian lenny main
As alternative, you can upgrade to Debian Squeeze. In that case substitude lenny by squeeze in the original, unmodified /etc/apt/sources.list and run the following commands:
apt-get update apt-get dist-upgrade