I've been getting this same error for the past 3 hours, even after Square-Enix posted that they had "fixed" the log-in issues.

I sent a GM message from an alternate account asking for assistance but they directed me with an automated message to the Square-Enix support center.

I don't really see what the support center could do for me what a GM in-game could not.

According to the chat on some forums, the Error Code: 3102 is related to your character still being logged into the game.
Normally after 5-10 minutes it automatically kicks you out and you can then relog back into the game.

However, in extreme cases the character does not disconnect even though the player is no longer present in the game.

From the horror stories I have read on some blogs, it took emergency maintenance to fix the problem, with some people having no access to their characters for days or weeks.

Square-Enix, please fix this by either forcing the characters still logged into the game to log out or with maintenance.