Another data point here. I have a Delta Reserve and a Delta Plat Amex. I have had little trouble using these in the past. I am taking the family to SLC to ski and am flexible on the dates. Every date that I put in on the online engine came back with an error message. I called 888-750-3284 an got an unhelpful rep who said that it was not available if the online engine said so. I called back to 800-325-1447 and got a very helpful rep who let me use these certs with no problem. All fares were LUT here. The moral of the story is that you must call. The online engine is now "broken" like the award calendar.