Comment 3 for bug 1437209

May be some explanation on when this happened.

I was experiencing a loss of GPG PUBKEYs as described by "Apt-get Reports NO_PUBKEY GPG Error for Keys that are Present in Trusted"

https://bugs.launchpad.net/ubuntu/+source/apt/+bug/1263540

Then I ran :

$ sudo apt-get install ubuntu-keyring --reinstall

This caused a crash while re-installing the ubuntu-keyring package.

Later I did proceed as explained by the latest posts on bug 1263540.

I deleted all the contents in /etc/apt/trusted.gpg.d/ (Not exactly) :

$ sudo mv /etc/apt/trusted.gpg.d/ /etc/apt/trusted.gpg.d.old/
$ mkdir /etc/apt/trusted.gpg.d/

Then I ran :

$ sudo dpkg -i webupd8/launchpad-getkeys_0.3.3-1~webupd8~2_all.deb

(launchpad-getkeys was found here : http://www.webupd8.org/2010/05/automatically-import-all-missing.html)

$ sudo launchpad-getkeys
$ sudo apt-get update

... This solved the issue for me.

Still the ubuntu-keyring is not broken and performing well.