I've been trying to both sign-in and authorize my account on a different PC. I can access the iTunes Store fine. But when I go to sign-in or authorize the PC, I get a "fieldname: null. unknown error" message on the sign-in screen. I tried signing in on my MacBook, through iTunes by clicking my account name, and I receive the same error there. Anyone else having issues? I've emailed iTunes Support.. we'll see how long it takes for them to get back to me. Sometimes they respond within minutes, sometimes they take a day or more. Apple REALLY needs phone support for iTunes.