@gilou24 Your web server or cache configuration is loading an old version of this required file (from a previous version of the plugin)
https://www.un-jardin-bio.com/wp-content/plugins/wp-customer-reviews/js/wp-customer-reviews.js?ver=3.5.1
In the actual 3.5.1 version, the text “ajaxAct2” will appear if you search the contents, but it does not appear in the version running on your site. The version your site is serving appears to actually be prior to 3.5.0 so it’s definitely something with cache on your site (a plugin?).
The expected file: https://plugins.trac.www.ads-software.com/browser/wp-customer-reviews/trunk/js/wp-customer-reviews.js where you can find “ajaxAct2” if you search the contents.
I have no insight into what caching plugins or web server / hosting caching might be in place, but they appear to be ignoring query strings on JavaScript / CSS assets, which is going to always cause you headaches.
If you have a way of purging/clearing cache on your site via some plugin you are running, this should resolve the issue, but like I said, any time a plugin or WordPress itself updates, you’re going to run into issues if your caching system continues to ignore query strings ( the ?ver=# portion of the above URL )