Ubuntu 14.04: PPA key not found on keyserver

Running “apt-get update” ubuntu complains about missings ppa keys.

In my case I was trying to install Libre Office and the missing key was 83FBA1751378B444.

I couldnĀ“t find any key running:

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 83FBA1751378B444

The message that I gog in the console was:
gpg: requesting key 83FBA1751378B444 from hkp server keyserver.ubuntu.com
gpgkeys: key 83FBA1751378B444 not found on keyserver
gpg: no valid OpenPGP data found.
gpg: Total number processed: 0

The solution to me was running:

 sudo launchpad-getkeys 

and the I could finally run “apt-get update”.