Flight 2318, ORDo DCA, leaves an hour late on Thursday 2/17, no big deal.Pilot announces special DCA rules of seat belt lights on no john trips last 30 minutes, no big deal. Pilot announces 30 minuteds to land. 40 minutes later he says we are landing at IAD due to a "procedural problem." After we land police cars pull up. I am in first and hear the captain saying something about getting to ORD late and not having the right passwoord. At one point he shouted his date of birth into the phone. He anounced that: "Due to security" there are certain things that are required and something was amiss, "That is all I can say." Wierdly we DID NOT HAVE enough fuel to get to DCA and spent another hour re-fueling. We then flew from IAD to DCA. Bet that is the shortest AA "segment" anyone has ever flown. What do you gurus thing actually happened to make us land at IAD?