App store asks for password, which I enter, over and over again

Downloaded Mavericks (took 5 trys), trying to update iPhoto but the issue is that when I hit "update" it asks for my password, which I enter, and it drops down and asks for my password like it was incorrect though it was not. I've now changed my password twice, just to make sure, and I've typed it over and over again and nothing happens. I've signed out of the app store, out of the itunes store, and out of icloud just for good measure. Then I try to sign back in and it still happens. Anyone have any suggestions? Thanks very much.