Same here, I was online to do a round of logins on my mules for the "Repeat Login" campaign, and suddenly was dropped out. At first I was getting a "protocol error", but now it's "Error code FFXI-3100: Could not connect to lobby server."

From reading old error reporting on Alla and Blue Garter, it's probably not anything we can fix. It could be a third-party ISP that SE uses to connect accounts and servers, and could be hours or days before it is resolved, due to the fact that some can still log in and others (like us) cannot. It's not that the servers are down, it's that a small sub-set of users cannot log in.

Ever try to let SE know there's an issue? Good luck, they have the ultimate firewall between users and staff who could help us. They will not even admit a problem exists unless it affects an entire server population.