Hi Hervé
Updating your template to the latest download should resolve this issue for you. For details on updating your template may I suggest the following article..
https://joomla51.com/tutorials/joomla-basics/updating-your-joomla-template
If the issue persists after updating, may I suggest sending temporary administration access to your Joomla installation to info@joomla51.com and we will examine this issue further. For our reference please paste a link to this post in your email.
Ciaran