I have read your thread and I had almost same problem just few minutes ago and that is how i found this forum.
1. Registration problem
My problem was that my friends were able to register on the website, they got the invite and confirmation emails but when they then clicked on the registration link the got ERROR. I solved it by going to BuddyPress (in the dashbord to the left under General Settings) – Page. There you can see REGISTRATION two options Register and Activate. Make sure the dropdown next to Register says REGISTER and the dropdown next to ACTIVATE says ACTIVATE (Do not mix it with the Activity Streams below otherwise it wont work)
When changed the dropdown to ACTIVATE it worked and my friends are able to register themselves now. I hope it solved few of your problems.
2. Sending invite and confirmation emails to your invited friends
Make sure you install the plug in INVITE-ANYONE under Plugins. Because that plug in together with the registration form works together for sending emails and completing the registration.
Hope this helps and solves your problems as this is an amazing platform.
