bbPress.org

In fact, in the source of your WordPress site, there are a bunch of links that result in a 404, and they all have wordpress in the URL.

404 Page Not Found:

http://subventions.fr/wordpress/

So, in your WordPress control panel, I suppose this could be wrong:

Options->General: WordPress address (URL)

I think your problems exist with the WordPress setup, and they are showing up now with bbPress integration.