same here, same problem same attempted solutions.then i contact aarp support, and a week later i get a response to try again. It magically worked again, i was able to purchase gift cards, they did not tell me what the issue was. 

I managed to purchase 2x$500 cards. ever since then i keep getting the error message  "There was a problem with your payment. Please try again or contact AARP Rewards Customer Care at 1-866-451-6305.Please note, even though there was an error with th...