Error doing sudo apt-get update Xubuntu 12.10

view story

http://askubuntu.com – I keep getting this error every time I do sudo apt-get update in the terminal. Also I'm completely incapable of installing anything through the terminal, even after adding the required, up-to-date repository using the add-apt-repository command. Any help will be appreciated. GPG error: http://packages.ubuntu.com quantal Release: The following signatures were invalid: NODATA 1 NODATA 2 (HowTos)