If the error above appears for your Recommendation page, it indicates that you have not registered a recommender in your application. You must register a recommender for your application to be considered complete.
If your recommender has not yet submitted their recommendation or will not be able to submit your recommendation on time, you should still submit your application prior to the deadline. You do not need to wait for your recommendation to be received before you submit your application. Your recommender should do their best to submit the recommendation as soon as possible.
Follow the steps in this video to learn how to register a recommender: