Agree with jason8612 on the communion thing, but the hotel is only fully booked for the Thursday (26th) and Friday (27th) night. It is available starting Saturday (28th) night.
I actually think this is to do with a conference held at the Sheraton during those dates and the hotel blocked rooms so the participants can book it. As most likely not all of them will sell, they'll get released back into inventory at a later date.
You can always e-mail them and ask.