gnupg - What is the easiest way to resolve apt-get BADSIG GPG errors?

I frequently cross this issue, and always have to google for an answer. Does anyone have a permanent fix for BADSIG errors from apt-get?

W: GPG error:
http://download.virtualbox.org lucid
Release: The following signatures were
invalid: BADSIG 54422A4B98AB5139
Oracle Corporation (VirtualBox archive
signing key)

Here's the (easiest) solution:

Type the following commands in the Terminal:

$ sudo -i
# apt-get clean
# cd /var/lib/apt
# mv lists lists.old
# mkdir -p lists/partial
# apt-get clean
# apt-get update

Credits: ubuntugeek.com

Edit:

If the error occurs again (maybe after a few days/months), open Nautilus as root > navigate to var/lib/apt > delete the "lists.old" folder > then open the "lists" folder and delete the "partial" folder. Now, execute the aforementioned commands again.