BIG-IP Virtual Edition Configuration Utility log in failures

And here is the full text of the error message that is given in the pop-up window:

Authentication required!

This server could not verify that you are authorized to access the URL "/tmui/logmein.html". You either supplied the wrong credentials (e.g., bad password), or your browser doesn't understand how to supply the credentials required.

In case you are allowed to request the document, please check your user-id and password and try again.

Error 401