I believe this is because their ticketing system is not up to date regarding available tickets. Despite having them in the basket, they are not available, thus payment fails.
It takes too long to refresh availability.
True.. I think I've been waiting on the list since 2011.. 8 years now. I'm number 15xx (don't remember exactly) and year ago I was 19xx, so I moved up 400 places in 1 year. Couple of years ago I moved over 2000 spots so I'm not sure how that works... Every year I think it's just one more year..
Tickets opened for sale to members today, about 1 hr ago. They are almost all gone now so I dont expect to see any available tomorrow to public.
I may have 4 spare tickets if my family doesn't come.