Encountered the above error. Looked at this thread:
I followed this thread, and it removed the error. When I tried to place the next order, the order "completed" without me being taken to PayPal at all. The status in the system is still 'Pending' so at least JoomShopping does not think the order is complete.
When I came back into the configuration to reset this value, the 'Payments' icon is missing. WTF is up with that?