ludo974
Hi,
Actually, it due to the configuration of article on your site only. In this template, the article page will show 'introtext' in blockquote format. However, that article on your site doesn't have introtext so that Joomla considered all text of that article as introtext and you saw that duplicated content.
I just disabled option to show intro text in the backend settings of that menu item 'Inscription en ligne' and it's showing fine now.