Ad Unit installation

Hello, I am using twenty twelve theme. I was approved by media.net and trying to install their ad unit to my site http://www.the-gorod.com. I’ve tryed different locations, text widgets and sizes, but the unit always shows at the very button, under my footer, on the left. They say it is nothing to do with their code, can any one suggest what is the problem?
Thank you very much

P.S.: I am also using Chitica and it works just fine