We stayed at the Grand Hyatt during the last weekend in April, 2008. Like yourself, we won a single queen bed room. I e-mailed a week before asking for two doubles only to be refused. Got to the hotel walked up to reception and to our surprise the check in assistant offered us a choice of either a single queen or two doubles without me even asking. So, hopefully (fingers crossed), if you are unable to secure a double before you check in you still maybe offered a twin room upon on arrival. PS. I'm not a frequent hotel stayer but the Grand is a really nice hotel, in an excellent location. Have a great trip