Less frequent travelers may not know that many credit card companies will act as if you using your card away from home is someone else using it, and deny the charges! It's part of fraud protection initiatives, but it can make life difficult when you're trying to legitimately use your card. I first had this happen to me when on a trip to the Grand Canyon; as I pointed out to the service representative when I called to find out what the problem was, the whole idea behind an airline affinity card is that you're traveling away from home!
To avoid this annoying and embarrassing experience, call your credit card company and let them know the dates and locations of your travel. That way when you find something amazing in Aruba you'll have no difficulties buying it!