I have had the same problem since my ADR window opened on Friday. All in all I have only managed to book 3 ADRs online, out of a 14 days stay on a DxDP. I have had to call the Dining line every day. They are very efficient I have to say, but I would prefer to be doing it online, and I wonder what the point is of having the online system. At first I thought it was volume of customers trying to use it at the opening time each day, but I have tried at all hours.