I installed wordpress in one directory and the thumbnail scroller worked just fine and then I moved the frontend of my website to the root and kept the wp backend in its directory (not the root), since then everything on my website is working just fine, but the scroller doesn’t work anymore.
This problem is from your server.
Please contact your webhosting company and tell give permission for loading this link to fix this error:
XMLHttpRequest cannot load http://test.promaquette.fr/wp-content/plugins/dopts/frontend-ajax.php. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://www.promaquette.fr' is therefore not allowed access.