Insufficient Permissions to Enable the Membership Plugin

WordPress is up to date, and I have deactivated all other plugins and activated the standard Twenty Twelve theme, yet, when I Network Activate the Membership Premium plugin (3.4.4.1), I get a red notice in the admin saying: "The Membership plugin is not enabled. To ensure your content is protected you should enable it". When I click "enable it," I get the standard gray error page saying: "You do not have sufficient permissions to access this page."

How can I resolve this error and use the Membership plugin?

Thank you!