Dear Pascal,
The first thing you can do is update your WordPress installation to the most recent version, 3.4.2. (which is always a useful thing to do, they offer important security updates and other fixes with every new version) – and try the preview again. If the error message is still there, and you don’t want to risk it, you can send me an email with your website’s admin login/password to support@satoristudio.net (no disclosure guaranteed), and I will debug and activate the theme for you.
Sincerely,
Andrew | Satori