Need more information!

If you were Plat last year, then you are still Plat until Feb 28. As Plat you should be able to get a room even if they are sold out with your Plat override. What dates? Do you mean no award availability on those two nights? Is there a special event going on at the time? Is this a second room you are trying to book, as Plat override is only for 1 room? Were you signed into Marriott.com when you attempted to book the missing nights? Did you try booking the missing nights as separate 1-night reservations while you were signed into Marriott.com? Was this a special room type (like a suite) for which Plat override would not work? As I said earlier, need more info to provide useful feedback.