I am getting below GPG error on running the command
sudo apt-get update.
W: GPG error: http://in.archive.ubuntu.com precise Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <firstname.lastname@example.org> W: Duplicate sources.list entry http://archive.canonical.com/ubuntu/ precise/partner i386 Packages (/var/lib/apt/lists/archive.canonical.com_ubuntu_dists_precise_partner_binary-i386_Packages)
Also, I am not able to install applications from software center. Every time I install it shows a dialog box with the message,
Requires Installation of Untrusted packages
The action would require the installation of packages from not authenticated sources.
OK or Repair options does nothing.