This can happen if you started an application for athletics (example only -- really any application within ParentVUE, but this is the most common, having opened for winter sports last Monday), but did not finish & submit it. The system only handles one application at a time.
If you find this is the case, finish & submit the athletic one (or delete it and come back to do it later), and you should see the 8th-grade HS programs application appear as an option (along with athletics, etc.) when you go back to the main ParentVUE page & again click on online registration.
Not saying it's a good system, but it's the system they have...