The Reservation Guarantee is for standard rooms, not suite or specialty rooms. Also note that top level suites (like Presidential suites) quite often can only be reserved directly at the hotel and not the general Marriott reservations center.

With that said, if you are trying to use the guaranteed room reservation (48 hrs or more in advance), I would suggest using the online booking tool. It bypasses the hotel and the regular Marriott reservations center. Unless the hotel has received a waiver directly from Marriott for the night(s) you are trying to reserve, the online booking tool will automatically get you a standard room. Note this is part of the reason local hotel staff don't like the Reservation Guarantee as the hotel doesn't have any direct control over it and it can get them into oversold situations (even when the hotel management didn't want to do that.)