I've run into the same issue before. It is an internal reservation code. Will never work on the internet. What I do is make a list of the dates that you are planning to stay and then just call the Reservations line. Tell them you are going to make a series of reservations and then bang thru them. If you get a someone that knows what they are doing, it'll only take 15 to 20 mins to make 10 to 15 reservations. I normally book months in advance if I know that I'm going to be someplace for a while. The reason for this is the possiblity that the rate code could get sold out (it's happened to me before).