I was busily mining away and my son was running missions when we were both hit with the issue this morning. Three of the four characters I had online were disconnected and now can’t log back in, but the fourth character can. And my fifth account can log on as well. Unfortunately I can’t find any information about what this error is specifically, but reading through the forum it seems to be affecting a lot of folks. No info from CCP yet, though it’s been nearly an hour since this started occurring.
 Took an hour and a half, but CCP finally fixed the issue by conducting an emergency reboot. All of my characters are able to log back in.