Well yellow, i just noticed that when I enter the product url directly in the address bar, say:

http://www.gemsoul.com/star-ruby/1-0...ntreated)-p-37

and then add it to cart, it works fine.

However, when from the main page, I click on the product, after the url there is a suffix of zenid (example: ?zenid=727268057a2a96585f5e3316c4e37501). Now with this suffix, when the product is added to cart, it shows the message that shopping cart is empty.