Ubuntu 12.04 can't install Firefox 13 update, because the package is corrupted. While attempting to install, returns this error (I translated it from my language to English).

 /var/cache/apt/archives/firefox_13.0+build1-0ubuntu0.12.04.1_i386.deb

    W: Waited for dpkg --assert-multi-arch but was not there - dpkgGo (10: There are no "child" processes).

I can tell that the package at /var/cache/apt/archives/firefox_13.0+build1-0ubuntu0.12.04.1_i386.deb is corrupted, but even as admin, I can't delete it in order to be downloaded again.

How should I proceed?

EDIT: There was a single package causing this conflict, please report here to understand all the situation: Why can't I install from software center?