UPDATE: The actual event invitation says the event is 12/17, and the Craigslist ad says 12/31. To be on the safe side, show up for both.
UPDATE 2: Ronn himself emails: "Speech I am making for a non-profit organization is 12/17. It's a charity running the event that asked me to speak not an event we run." In a second email, he adds, "All I am doing is showing up for a speech for a charity."