The last time I was there the same thing happened to me. Neither a gift card or the Disney Visa Rewards card worked at Epcot making me pay with a credit card. I tried again next at Disney Springs and the employee at Morimoto Asia said that they couldn't be used but a regular credit card was no problem. I then tried to use the Rewards Card to buy tickets to Haunted Mansion at an AMC theater last year and it didn't work again. I've always assumed it was a scam to make you buy gift cards or accumulate rewards points and then not actually use them so this sounds about right.