I have three of the 2012 summer Promotion Free Night - Category 1-4 hotels certificates, and was looking at the Marriott Mexico City Reforma, (currently a Category 4 hotel) for early June 2013. I noted that it was not bringing up the summer promo certs as available payment. Is this because it's not a US property, or because there's a PointSaver promo during that period?
Were you trying to use all 3 certs on the same reservation? If so, that may be the issue. A buddy of mine that is a recent Marriott Rewards member scored 4 free nights over the last two promo periods. He wanted to head to Florida with his wife. He tried booking, with the certs, through the online site, but it never gave him that option. He called the helpline and they hooked him up.
I've "tested" it successfully on other properties; up to three nights and it gives the option to use my certs, over that and there's no option at all. I'm probably going to use them elsewhere (stateside), but I was looking around at other places to take the missus this spring.
After some more poking around and experimenting, it seems that the PointSavers offers are the culprit. I checked other properties in the US and abroad, and the summer promo certs worked everywhere except where there's a PointSavers deal during the reservation timeframe. I don't know if that's a program rule, or just an unexpected consequence in the booking engine. It'd be nice for someone from Marriott to chime in with a definitive answer (and maybe some reasoning). No big deal, but a nice-to-know going forward.