Comment 51 for bug 497299

If you lack /etc/init/network-interface.conf, something is very wrong with your packages. This bug is about issues in Karmic resulting from the update to fix bug 461725, and you seem to be running Lucid (according to your apt-cache policy). However, on top of that, ifupdown version 0.7~alpha3 appears only to be available from the Debian experimental repositories. You need to be running an Ubuntu version of this package.

To restore your system to Ubuntu-only packages, try this script with sudo:
  http://bazaar.launchpad.net/~ubuntu-security/ubuntu-security-tools/trunk/annotate/head%3A/utilities/downgrade-all

It will install the "lsb-release" package if you don't already have it, and then it will attempt to downgrade anything not in the standard Ubuntu repositories (ignoring any custom /etc/apt/preferences, and any 3rd party repositories, including PPAs, etc). It will prompt you before the downgrade, but please read and use it carefully!