Seriously, have you encountered this error message before?
This error occurs when a person attempts to use the same browser with multiple tabs to log-in as different identities. (e.g. a real user from AD and amadmin)
Honestly, in my many years of Sun AM/OpenSSO/OpenAM deployment, I have not encountered this error once. This is because I know exactly one should not use the same browser to log in as different users.
However, today is an exception! :) I'm so blur today.