An exam lockout can occur if you have exceeded the fail limit of an exam within a course. In the even that you have been locked out of the exam, the course will reset itself. This means that all progress made on the course will be reset back to the first page of each chapter. You will then have to go through all of the Required chapters again in order to attempt the Exam again. After an exam lockout has occurred, there may also be a set amount of time before you can attempt an exam again. This can be found in the Exam section of a course.