I was logged into chat and Math.SE, but I needed to reset my connection. When I tried to log back in, I could connect to Math.SE, but chat.stackexchange.com would not recognize the same login. I use OpenID and Google to log in, and the email address for OpenID shows up under My Logins.
When I try to login I get this screen (I have removed my email address, but the email address that was removed shows up in
my logins). I used this same login to access my non-chat accounts.
A few minutes after posting the last edit (with the image above), I was able to login to chat. I didn't do anything other than try again.