Got this recently from Marriott:

Unfortunately, the property does not have any record of my reservation. I called them and they told me that when the system switched over, all Marriott reservations were lost. I am working with them on a new reservation and they have confirmed that they will honor the rewards stay - just an unexpected headache to get it all straight... I will fell better once i get a new confirmation from "The Grand City Hotel Salzburg" the new name.