I think maybe you should check with your company then. If you've entered the correct code in the Group/Corp # box, and no special rates come up, then you have either entered the wrong code or there are no corporates available.

Also, note that sometimes corporate rates are dependent on which day of the week you are staying there or even how many nights you are staying. For example, my corporate rate is only valid at the Hyatt Logan Airport, Mon - Fri, and not on weekends.