New User sees a Membership-Notification?! (BuddyPress + MU + MemberShip + ProSite + Easy Blog)

So I have a multisite with a free and a pro membership. But when the Pro-User is in the Backend, he sees “The Membership plugin is not enabled. To ensure your content is protected you should enable it” and “You are logged in as a Membership Admin user, you will therefore see all protected content on this site.” – how can that be?