What can I do?

[skankerror]

in fact this not a problem.
It's just that you don't have GPG keys of a launchpad repository.
This is a warning, not a fatal error.

A simple way to do is to install this http://archive.getdeb.net/install_deb/pl...b1_all.deb

then in a terminal type :

$sudo apt-get update

don't worry about GPG error, then

$sudo apt-get install vdrift vdrift-data