thanks jason,
i narrowed the cart issue to the following. when i process an order and it goes to the order success page. everything looks good, it show products order and details of order submitted. when i navigate back to the the store some how it is storing the products in session along with all other session varables. so when i go through the checkout process through paypal it doesn't process the order. i am assuming the token is expired. my question how do i clear all cart and session values, after my order is successfully gone through? i added the clear cart to the checkout_success page but it didn't work?