I have tried to check out the RSVP feature on your demo site.
When hitting the "Attend" button, however, I always get the error message:

0
CANNOT ASSIGN BY REFERENCE TO OVERLOADED OBJECT
OH MY GOSH! YOU FOUND IT!!!
Looks like the page you're trying to visit doesn't exist.
Please check the URL and try your luck again.

Logged in as "user1" and "user2". Have tried both Firefox and Opera.

We're very interested in this feature, but before joining the Gold club I would like to test the feature. Please fix the demo!

Thank you!