GPG error in apt-get update

When I want to install the SMPlayer from http://smplayer.berlios.de/downloads.php?tr_lang=en,

I have a problem which is

W: GPG error: http://ppa.launchpad.net hardy Release: Release: The following signatures couldn’t be verified because the public key is not available:  NO_PUBKEY @@@@@@@@@@@@

The solution is

gpg --keyserver subkeys.pgp.net --recv @@@@@@@@@@@@
gpg --export --armor  @@@@@@@@@@@@  | apt-key add -

by using the following references 

http://mr-dust.pe.kr/entry/ubuntu-gpg-error-related-launchpad-ppa
http://my-it-dump.blogspot.com/2009/02/fixing-gpg-errors-nopubkey-in-apt-get.html