I had the same problem when I set attribute phone (in address) required. All old accounts without phone number got Server Exception 500 when placing order. Filling in phones in backoffice clients->addresses solved problem.
I have defined discounts in Catalog Price Rules. Information about discount is visible on product page: But there is no information about discount in cart view: In confirmation mail which is sent to customer after order finalization there is also no information about discount. How can I display even small information that discount is included in price?