I alse have the same problem as in topic: "Can not see any Admin to block from accessing the editors" (http://wordpress.org/support/topic/can-not-see-any-admin-to-blocked-from-accessing-the-editors?replies=10).
I tried creating new admin users before and after plugin activation. I tried login in and out with all admin users. But I cannot see any admin user in the selector for blocking.
Can you help me?