Error with the shopping cart

[The big]

Hello,

I need a bit of help here.

I have just allowed products that can be shipped.

When a product added to cart I get this message :

Error the quantity of the product for calculation is 0, please notify the shopowner, the product id

Any thoughts how to fix this?  I am using Joomla 2.5.6 and Virtuemart 2.0.8e