You put Contact Form 7’s shortcode inside another <form> </form> element. Remove the <form> and </form> as you don’t need them at all.
Well ok… Stupid error again ! Thanks for the help ! It’s working now !
You don’t have Contact Form 7 on the site.
Well sorry, I had to find a provisional solution.
By the way I created a test page here with the Contact Form 7 at the bottom : http://www.juliendemelenne.com/index.php/contact-test/
It’s still the same issues when I want to send the message…
Here: http://www.juliendemelenne.com/
The form is at the bottom of the front-page