Ubuntu Linux: BADSIG error for openprinting

• Description:
  

  W: GPG error: http://www.openprinting.org lsb3.1 Release: The following signatures were invalid: BADSIG 7A4B44C2D2A2203E OpenPrinting (OpenPrinting Test Key) <webmaster@openprinting.org>

• Solution:
  edit /etc/apt/sources.list, and replace

  deb http://www.openprinting.org/download/printdriver/debian/ lsb3.1 gutenprint

  with

  deb http://www.openprinting.org/download/printdriver/debian/ lsb3.2 main

  then run

  sudo apt-get update