Signature Errors on Ubuntu repositories

On all of the Ubuntu installs I’ve ever had, I almost always eventually run into the following error when running the ‘apt-get update’ command or hitting the ‘Reload’ button in Synaptic.

Error:
W: GPG error: http://nz.archive.ubuntu.com hardy-updates Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key
W: You may want to run apt-get update to correct these problems

From what I understand the problem comes from apt downloading an incomplete/corrupt signature file, meaning that the signature then doesn’t match that of the packages. The fix at the moment is to simply delete the incomplete/corrupt signature file and download it again. To do this run the following command:

sudo rm /var/lib/apt/lists/partial/*

Afterwards running apt-get update doesn’t return the same error.