I'm trying to redeem a $25 iTunes gift card on my Mac Mini (running Mavericks and the current version of iTunes). But every time I clink on a Redeem option, I'm asked to enter my account info. Which I do. I know I'm signed in because a remaining balance from the last purchase I made pops up in the right-hand corner. But nothing else happens. I click Account or Redeem again, and the request to sign in appears again, as if I weren't signed in. Lather, rinse, repeat. (If I sign out, the remaining balance disappears, so that part at least is responding.) I've made sure I'm not running either Chrome or Safari in private mode. I've quit and restarted iTunes. I tried resetting the iTunes cache in the Advanced Preferences, although the button just sort of blinked when I clicked on it, so I don't know if anything really got reset.... Anything else I can try to get iTunes to actually work with me, instead of signing me in and then pretending I'm not signed in?