title: Magento cart can only take one item
body: <p>Our cart is facing the following issue - you can add one item to the cart - but not a second one. I have already check all the obvious in the system section for restrictions on the quantity (e.g. <a href="https://stackoverflow.com/questions/15239431/unable-to-add-product-quantity-more-than-one-items-in-one-order-magento">Unable to add product quantity more than one items in one order MAGENTO</a>) - cookie life time - and many more. No misconfiguration was found. I am using Magento 1.6.2.0. The error was reproduced in Chrome and Safari on Mac OS X many times in a row. I am sorry that I can not post an URL. Moreover there is to know that the run-time environment is an Amazon EC2/RDS Service.</p>