Did you check requisite courses, enrollment holds, instructor consent requirements, and other prerequisites before you generated your schedules? If not, and any of these conditions exists with the classes you chose, you will see an error message when you attempt to enroll. Be sure to review the online Course Listing to check for requisite courses or courses that require instructor approval. Talk with your advisor or the instructor to obtain permission numbers if needed. If you already know exactly what you want to take, you can simply enroll as normal through PeopleSoft.