[chrishajer]

This does not appear to be correct:

$bb->wp_siteurl = 'http://www.subventions.fr/wordpress';

Your wordpress site comes up at http://www.subventions.fr/ so the wordpress part is superfluous. I think you’ve got a path problem somewhere. Normally you install bbPress like this:

/var/www/subventions/wordpress/

maps to http://www.subventions.fr/

/var/www/subventions/wordpress/forum/

maps to http://www.subventions.fr/forum/

forum is a subdirectory of wordpress in a typical integrated setup. Is that your setup? If so, then your config is wrong.