Force quit iTunes in that case. That's the great thing about OSX & its ram management, it will close off that part of ram so it doesn't affect other apps. You can simply re-open iTunes. (After you've forced-quit an app that ram will also free up.) As murasame was suggesting, if you get the chance, restart the comp (in safe mode & repair permissions) might clear up some issues. Safe Mode & Repair Permissions (click me.) Disk Utiltiy can repair permissions. What happened to you may have been just a one off event, else a permissions issue, else directory issues.