Ubuntu apt / PPA, add repository examplesetc...

this is a common problem with Launchpad PPAs. Common enough that I've copied these commands to use when I reinstall or add new Launchpad PPAs.

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys  
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys YOURKEYNUMBERHERE  

sudo add-apt-repository ppa:stebbins/handbrake-releases
sudo add-apt-repository "deb http://archive.ubuntu.com/ubuntu $(lsb_release -sc) universe"

add, fetch repo key

apt-key adv --fetch-keys http://www.4pane.co.uk/4Pane.asc
or
wget -O - http://www.4pane.co.uk/4Pane.asc | sudo apt-key add -