rcraw - The website might show availabiity that isn't really there, then not let you book. (Not that a CM should have been rude about it) It's just one more joy of a really disfunctional website.
Call Disney directly. In spite of the occasional problem CM, most of them are happy to answer all of your questions. If you get someone rude, feel free to call back and get someone better. Of all the ways I've booked, online through Disney has always been the most troublesome later and I won't do it again.