Marriott.com won't accept reservations under my corp code past the expiration date - always a pain because I have February meetings and the rate expires in February, get's renewed right close to year end (by which time the hotel might be full).

Not sure how he booked it, but it's nothing like using a corp code for which he wasn't entitled to use it.

Maybe he booked a room at the prevalent rate, and then tried to get it adjusted. But if he has a written confirmation, then the rate should be honored for existing reservations (without any changes allowed).