If the user is redirected to shopping cart directly, this means there is a jQuery conflict in this page to avoid adding product to cart with jQuery AJAX loading.
Virtuemart "add to cart" button adds the product to cart with AJAX loading, if that fails to work, it goes to shopping cart (it is a good thing and it is a protection, otherwise nothing will happen.)
You need to investigate your website against "jquery" conflict with Mozilla Firefox Firebug plugin, to figure out what causes this jquery conflict in this page:
www.aromesdemae.com/detalles-y-regalos
Having an extension that differs from
www.aromesdemae.com/aromas/floral/huile-d-olive probably causes the conflict. For instance, slideshow, slider and other things that loads additional jQuery library would most likely cause the jQuery conflict.
Look here
www.flexiblewebdesign.com/forum-virtuemart-2-template-puremart-support/523-the-easiest-way-to-solve-jquery-conflict-issues
To solve the jQuery issues in the website entirely. This is the best and easiest way if you have no experience in coding.
Regards.
Forum Support.