After installing the plugin, I saw no link to the invitation. I reinstalled all the components, including MU and BP. Then change the date of registration in the database administrator and user for a year after today's date. I saw a reference to the invitation. This is good. Invitations are sent successfully.
But when you try to go to the link, get error. Links are different forms for the registration of the invitation. This is a wp-signup or bp-signup. Because I use BuddyPress, I point bp-signup. But even if you specify the wp-signup, all the same error.
If the link http:/example.com/bp-signup.php?example @ example.com, then I see a 404 error.
If the link http:/example.com/wp-signup.php?example @ example.com, then I see the error: Fatal error: Call to undefined function is_user_logged_in () in / wp-content/mu-plugins/secure_invite.php on line 14
What is it? :( I need to create a closed network based on MU + BuddyPress, and nothing comes out. Sorry for my English.