I'm running Lion 10.7.2 on a late 2009 MacBook Air. The problem I describe happened just after installing the most recent iTunes and Safari updates. 1. At "choose account" log-in screen, when I choose ANY of the regular user accounts, OS X accepts the password, then loads a gray screen, and a few seconds later goes back to the "choose account" log-in screen. 2. I am not entering the wrong password. OS X still gives the shaking password box when I enter the wrong password. That's not what's happening here. 3. I can log in to the guest account. It's the only was I can get past the log-in screen. Any idea what's happening or know of a solution? I've tried resetting PRAM. My apologies if this has been answered before. I couldn't find any references to this precise log-in problem. Thanks for any advice.