It sounds like you have alternative challenges set up on your site! This means that your site is set up so that someone may enroll in one or the other of these programs, but not both!
In this case, you can help by doing the following:
- Go to People > Find a Person.
- Enter search information to find the reader.
- Click three-prong icon next to the reader's name.
- Un-enroll them from the incorrect program by unchecking the the checkbox next to the challenge they wish to leave.
- Enroll them in the correct program by checking the now visible checkbox for the correct challenge.
Note: You cannot unenroll someone who has already completed a program.