I'm getting "You do not have sufficient permissions to access this page." when enabli

A client of mine purchased Membership to use with the BuddyPress Social theme. The message appears in the dashboard that Membership is activated, but not enabled. Clicking on the link to enable Membership results in the following error message: "You do not have sufficient permissions to access this page." I have deactivated all plugins (except Membership, of course) and the error persists. I have switched from the BuddyPress Social theme to Twenty Fourteen and the problem persists. I searched the forum, found the thread about adding constants to wp-config and added the constant to specify the membership admin as my client's user name. The problem persists. Any ideas would be appreciated. The client is anxious to get this site up and running.