Got the latest itunes but it keeps asking me the password when I try to make a purchase. Not once but over and over. I enter the password but itunes ignores it and asks for the password again and again and I can not complete the purchase. The password is correct as I have verified it from my keychain. Capslock is not set. I can go to my account and check the account info is correct but still can't make a purchase.
I am having the same trouble since the update.
If you sign out of iTunes store and sign in again, it will/should work. It works for me.
Not a solution but a quick fix.
I hope it helps.