How to get Euro Truck Simulator 2 from GamersHell

I've been trying to download from this page (http://www.gamershell.com/download_109575.shtml) but it always gives me an "Authentication Key is not valid" error even if there isn't an option to enter one. This seemed to not happen on some other computers but for mine, it does. How can I fix this it is so f**ing annoying.