Just goes to show you the importance of backups and local copies that you can more reliably access.
Try in order;
Wiping the system partition from recovery mode.
Clearing the cache and data for the Samsung account from the Application manager screen (in the Settings menu)
Delete and recreate your Samsung account on your phone. Do not delete the account per se, just the info on your phone.
And as a last resort, if you are under time pressure.. back up anything important on your phone. Then write a 100% stock firmware image to the phone with the Odin software, followed by a factory data reset. Pretty much a sledgehammer approach that will fix pretty much any client side issues.