I've been told "The waitlist is closed" as well and it is enormously frustrating for a platinum. I kept on bugging them and eventually they could add my name to waitlist (apparently somebody had gotten their upgrade) and I catapulted to number #1 on the waitlist (per the agent). In the end, I got my upgrade. I disagree with the posters who say the waitlist should hold a finite number of names and don't see any logic or rationale to intentionally keeping the list to 20 names. The posters who have suggested that it's an IT issue are probably correct.