This is what i get when a customer tries to checkout... Any help?
Please check answer here:
http://forum.cs-cart.com/topic/42505-unknown-column-order-id-in-field-list-1054/?fromsearch=1
Note that in your case the query should be modified:
ALTER TABLE `12b_user_session_products` ADD COLUMN `order_id` INT DEFAULT 0 NOT NULL