Secure Invite Plugin – Page not found

This is probably a very basic question, but I have a very basic knowledge of WP.

I installed the plugin Secure Invite on my WP/BuddyPress site and when I test the plugin by sending an invitation email, I receive the message “Not found”.

I log off as an ADMIN and the link on the email points the user to: http://www.zesterandpeeler.com/register/[email protected]

What am I doing wrong?
Thank you!