iTunes sign in request infinite loop - tried many solutions already and still no success

Hi all,

After updating to iTunes 10.6 I've had a problem where iTunes gets stuck in a loop asking me to sign in to my Apple ID.

I am already signed in and it keeps asking me to sign in to activate Automatic Downloads. I enter the correct password and it simply asks me again. It just keeps going until I click Cancel.

I just subscribed to iTunes Match yesterday as well and it asked me for my password to add my MacBook Pro to iTunes Match. Same problem. It just keeps asking me. So I've now paid for iTunes Match and am unable to use it.

I am not able to add things to or view my Wish List either because it keep asking me to sign in to view or add to it.

I've tried deleting iTunes preferences which made it forget my Apple ID so I could sign in fresh. Same result. I tried signing out, quitting iTunes and signing back in. Same. I even tried restarting my Mac. Nothing.

I've contacted Apple via email but they haven't offered any solution yet. They just directed me to a couple of articles that told me what I already knew about signing in and using iTunes Match.

Any ideas?