iTunes and App Store keep asking for password.
If I log into the Mac App Store or iTunes to purchase an app/song I get prompted for a username and password, as expected; but then it just keeps asking. If I type in a purposly wrong password it will tell me it's wrong, but when I put in the correct one it seems to take it but the dialog just pops up again. This occurs on my MacBook Pro, my iMac and my MacPro. This also happens if I try to 'view account'. Every now and again I will break through this loop and see my account details, but if I try to change something, say my purchase methode, I get 'session timed out'.
I can log into the website just fine, I know the password is good.
Any ideas?
MacBook Pro, OS X Mountain Lion (10.8.4)