Theres is an issue related to "internet"...
Well, when you're connected on any chat and your connection is interrupted(by internet issues or whatever) you can't sign in if someone with higer rank than you don't kick out you from xat.
But this could be an issue, because it was supposed to send <dup /> to user already online, not the new one trying to connect.
So I think this could be fixed just disconnecting the old user(socket) already created before, and allowing the user to connect again without needed to be kicked.
Confirmed by some users on xat_test.
Mainly we brazilians that have a lot of internet disconnects are getting this error everyday.