This happens when you try to lock the door and you have a key on the inside or outside at the same time.
Take 2 keys, insert one first and unlock the door completely..leave this key in the lock and use the other key and insert it on the opposite side of the first key and unlock the door..you may need to use a little force. The barrel will then align. Remove the second key and try the lock, it should work..happens to me all the time :)
Paul, October 2009