CRE Loaded Paypal Problem

I have a problems with CRE Loaded, that i believe is a common problem. When a user selects to pay using paypal; 1) They are not returned to the website after making the paypal payment, there is an error - page not found. 2) The shopping cart is never cleared it always remains full even after the payment is completed. Even if they logout and log back in the items remain in the shopping cart permanently. (this is working if they select to pay by cheque/money order). 3) The order doesn't change to processed or completed in ADMIN. Also paypal ipn info is not available in admin. I need this fixed on a single website. I also need to know the step by step solution so that i can apply the same fix to my other websites that also have the same problem. Thank You.