I tried what I could-- messed with my firewall settings, uninstalled/reinstalled all of FFXI, un-linked and re-linked my characters on my Nasomi account (legacy something or other), I even tried to get "unstuck"... and so far no success.

So now, with summer right around the corner, I'm desperate. Halp!!

I'm able to get in far enough to see my main and my mules, but if I try and log in with any of them I get the dreaded 3101. What else could be causing my 3101 error?

Have you tried a VPN to rule out network problems? If not, consider that or try another network (such as a mobile hotspot from your phone) if you can. This will help rule some of those types of problems out.

Should only be 1 character per game account

Ah ha! That was it.

I still had two alternates linked under the same account from when I created the account a couple (a few?) years ago. Deleting them allowed me to enter the game.

Thanks for the responses!