I am currenly on the "You'll know it when it happens" quest and I have successfully protected the president from assassination. When I go and talk to Moore to get the next quest, She tells me to go and protect the president even though I already have. This is very frustrating and I have reloaded several time, each yielding the same result. This makes the NCR ending impossible for me as I can't leave the area until I have completed the quest. Although I can complete it, I cannot recieve the next one.