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I advise you to not close any pages, or close any tabs in your browser, just before publishing.
A 'session has expired' message means either that it is too long since you last logged in, or else that you closed the browser tab or browser window in which the login was done (which sometimes logs you off, with some websites.)
I think, though I am less sure of this, that the 'new user name and password' might be a bad case of nerd-speak gone wrong. Probably what is meant is, 'enter your user name and password *****'. That's certainly what it would mean, if you close a browser tab or browser window.