Probably a temporary thing. Last time I tried to order one, it gave me a date of the 14th of September (this was about a week ago). I'm sure they ran out of stock in their local warehouse, and are waiting for it to be replenished before you can order it again. The system is all messed up, so it doesn't let you order something if it isn't in the warehouse, but I wouldn't be too worried. Try again in a week.