Actually, Lane, it's a 48-hour CUTOFF, not a 48-hour WINDOW. What that means is that you're guaranteed a room (except in very specific circumstances that are quite rare) if you make your reservation 48 hours or more in advance.

Try calling the platinum reservations line rather than booking directly through the hotel. Although the hotel staff SHOULD know what to do, sometimes they're not as well-versed in special cases as they should be. Good luck, and keep in mind that you'll be paying the full rack rate (typically pretty high), but at least you'll have a confirmed room.