For those of you who are not seeing any corrupt characters, and are simply unable to log in with your credentials, I suggest logging over to the Square Enix Account Management site. Here you can just double check that all your login info is correct (Square Enix ID & Password, PlayOnline ID & Password). Now to address a corruption issue; once you're sure you can log in you may want to try Verifying the integrity of the system cache if you are using Steam. If not you're probably looking at reinstalling the PlayOnline Viewer. You can grab the latest one by accepting the terms at the bottom of this page.