Fix PPA Authentication errors in Linux

When running sudo apt-get update I often get an error similar to this:

GPG error: http://ppa.launchpad.net intrepid Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 0CF459B8DF37ED8B

After a little Google-ing I think I have found the answer. Fire up your terminal and try the following command:

gpg --keyserver subkeys.pgp.net --recv (ERRORKEY)

Replace ERROR KEY with the error code you are getting - it will be something like this - 632D16BB0C713DA6

Next type the following to add that key to your gpg keychain:

gpg --export --armor (ERRORKEY) | sudo apt-key add -

This resolved the errors for me, but I'm not sure it will work 100% of the time!