Several attempts to make a booking, tried entering via accorhotels.com and sofitel.com, using both Firefox and IE, all failed with "Please re-enter or fill in the missing information. The fields shown in red are either incorrect or are mandatory." -- but with nothing missing or highlighted in red.

EDITED TO ADD: After several more attempts I was able to make the booking by first changing my country of residence (to something other than the USA), then re-selecting USA. At that point a field for "state" appeared, highlighted in red. Selecting my state of residence allowed me to proceed. With luck this will help one or two people until such time as Accor fixes the glitch.