I' have another problem also undoubtedly connected.
If I select the menu ' NOS PACKS' and that I click on a product I' have like URL:
/les-algues-seches/mega-pack.html instead of /nos-packs/mega-pack.html

It indicates bad the category.

Link no SEO: index.php?option=com_virtuemart&category_id=2&flypage=flypage.tpl&manufacturer_id=1&page=shop.product_details&product_id=34&Itemid=50

The ID number 2 it' 'NOS PACKS' no 'LES-ALGUES-SECHES'

One note to vmcchk variable:

vmcchk is a variable added by VirtueMart and used for checking if cookies are enabled in users client agent.
You can disable this in VirtueMart Configuration / Core Setting / Enable the Cookie Check.
By disabling this, vmccchk will not be appended to URLs.