my experience has been to do the 24hour guarentee if the hotel is sold out. This had never been an issue before, they had always applied the corporate rate at check when I did this until now. Even at the same hotel a few months back, I did the exact same thing and they allowed the corporate rate. I guess they are now told that is not allowed to do anymore or something...

I dont know if the Diamond Desk can apply corp rates or not for just regular bookings I would hope that they could

Calling the hotel directly came on a suggestion from the front desk at the hotel, she said that way they could apply the corp rate, instead of not being able to because of using the diamond desk....