title: Prestashop : Error While updating product
body: <p>I'm using Prestashop version 1.5.5.0. When I try to update a product it gives me three types error sometimes internal server error, sometimes 504 gateway time out and sometimes blank page. When I activate developer mode I see nothing. In the error log of my server host I didn't find any error but sometimes it give "Premature end of script headers: php-stable". 
  I'm getting temporary solution of this problem by clearing smarty cache in the backoffice.
  I was running my website on fastcgi but for this problem I stopped using that. Can anyone shed some light on this ? My website is fast but the script is taking a lot of time to execute. Here is the website "<a href="http://www.allworldfurniture.com" rel="nofollow">http://www.allworldfurniture.com</a>"</p>