We have been getting emails from customers because once they were done completing the payment process at Paypal they were being redirected back to our site but were getting an error message. This issue has finally been resolved. If you are placing an order and paying via paypal and get an error, please let us know so we can look into it as soon as possible. Hopefully this takes care of the problem for good. Paypal made some changes without notifying its merchants ahead of time, so this is why the error was appearing.