I'm using Membership to control access to various online courses.
I would like users to be able to sign up for more than one course, but not in a linear, heirarchical fashion.
When I visit the page which shows all the available subscriptions, it seems as though a user can only be on one subscription at a time.
All other subscriptions are flagged with the message "upgrades not available".
I need these other subscriptions/courses to be available.
How to go about this?