OpenGraph and Like button

Dominik,
The Open Graph tags (what describe your page to Facebook) look to be setup just fine on that page. You can see how Facebook 'sees' it using their Debugger tool:
Facebook Debugger for your page

The image tag is missing, but that's simply because there's no image in your content. The only thing I'm seeing wrong about your page is that in the top of the right hand column, you're re-including the Facebook Javascript library again (all.js). That file is included by JFBConnect on all pages, and you shouldn't do it again as it can cause conflicts.

I don't think that's the cause of your problem, but it's the best place to start.

Hope this helps, but if not, just let us know.

Thanks,
Alex