When You Get A GPG Error Updating Your System

Sometimes you may get an error when doing apt-get update, just like this one:

W: GPG error: http://debian.linuxmint.com testing Release: The following signatures were invalid: BADSIG 07DC563D1F41B907 Christian Marillat <[email protected]>

To resolve this problem, you just delete all files in /var/lib/apt/lists, and apt-get update again.

Here is some information about `/var/lib/apt/lists/:

/var/lib/apt/lists/
Storage area for state information for each package resource specified in sources.list(5).
Configuration Item: Dir::State::Lists.
/var/lib/apt/lists/partial/
Storage area for state information in transit.
Configuration Item: Dir::State::Lists (implicit partial).

The solution is from the LMDE forum.