title: Prestashop - Unable to add the product (parsererror) when product has attributes
body: <p>I have a website using Prestashop 1.4.7.3 (and cannot upgrade it for now) and have trouble since 2 days when I try to add a product in ajax cart, this is the error message :</p>
  
  <blockquote>
    <p>TECHNICAL ERROR: unable to add the product.
    Details:
    Error thrown: [object XMLHttpRequest]
    Text status: parsererror</p>
  </blockquote>
  
  <p>I search the web since those 2 days and try everything i found (modifying content_dir, replacing mb_split by split, etc.) but nothing worked and now i don't know what to do and really need help.</p>
  
  <p>With Firefox and Chrome, I have no error on console tab, and only have this alert when i add a product with attributes or if there's already a product with attributes in the cart.
  When i click on "add", the cart is not refreshing and i have this alert, but if i refresh the page (with F5 or CTRL+R), i see the product correctly added.</p>
  
  <p>Can someone help me please ? Or give me a clue ?</p>
  
  <p>Thanks,</p>
  
  <p>Tony.</p>