I fired up the update manager today and received the wonderful error message of…
W: GPG error: http://ppa.launchpad.net intrepid Release: The following signatures couldn’t be verified because the public key is not available: NO_PUBKEY 60D11217247D1CFF
It sounds like this sort of message will come up from time to time. It is caused by the way signing of packages was changed recently. Here is a post about it on the launchpad site.
To solve the issue you need to import the signature to your local keyring. This is done with the following command to pull down the data.
gpg --keyserver keyserver.ubuntu.com --recv 60D11217247D1CFF
followed by this command to add it to your local keyring
gpg --export --armor 60D11217247D1CFF | sudo apt-key add -
You can do it through the user interface but the above command list is the easiest and quickest way.
UPDATED: WordPress keeps insisting on replacing – - with –. Sorry for anyone this has caused issues for. The commands have been corrected