My client has coursepress pro installed with a marketpress integration. Her users are required to create new accounts when they click 'enroll' on a course's page. The new account is subscriber level by default. Once authenticated, the new users cannot add the course (or other items) to the marketpress cart. This only happens for subscriber level users. If i am not logged in, or logged in as an admin level user, I can add items to the cart without issue.
NOTE: I have tried the patch to /marketpress/includes/common/template-functions.php available here