I dropped a class online and now I cannot re-add it. Why not?

Once the term has begun, the registration system does not allow you to change a dropped course back to registered status online. If you drop a course then wish to re-add it later, you must submit a Special Registration Form to the Office of the Registrar. If the class you dropped has become full, you will need the instructor's signature on the Special Registration Form to re-add the class.