Hi there. My problem was that when using wp-shopping cart when going to a new page the cart got empty. I managed to find the problem. For me was that i had a widget (text) where i placed a javascript. I removed the widget and everything worked fine. I knew that it was something realated to js not the server session settings as everything worked fine in IE. Hope this works for you too.
HI. This has something to do with wp-ecommerce. The problem for me was that i had a product category with no name. I deleted that one and everything works just fine.