I recently found out about this UI bug that affect RHLS-Standard users only. Essentially, the UI developers built the interface ontop of an existing learning management product. As such, it assumes (incorrectly) that someone would only need access to a course for the duration of a single individual class sale (90 days).

You should open a customer support case on https://access.redhat.com (setting the product to Red Hat Online Learning). Describe the behavior and error you receive and ask them to unenroll you from the class. Once that's completed, you'll be able to enter the class again for a fresh 90 days.

-STM