You are getting this message because you have not "marked as complete" 100% of the sections prior to the section you are attempting to access. You need to "mark as complete" each previous section prior to moving on to the next lecture. For sections containing video lecture, you need to view over 90% of each video.
Because you are earning continuing education credit for taking this course, including video lectures on teachable, we are requiring that video lecture be viewed in their entirety prior to moving on to the next section. Without this requirement, we would have no way of verifying that our registrant did indeed view a whole lecture, and the video lectures would become functionally optional, which is not our goal.