Just called my bank after getting this error tonight, a few hours after paying my subscription to FFXIV's fanfest premium LIVE streaming.

It turns out I was right. The errors 401 and 601 on the account management were caused by the fact that the CC was already in the process of being locked by my bank for suspected fraud, and the transaction that raised this suspicion was the TwitchTV subscription to the Premium streaming for the FanFest.