Does the URL you are inputting actually resolve correctly from the same client that is running Excel? Please verify that is the case via your web browser.
Within IIS for the web adaptor, under Authentication is Windows Integrated Authentication set to 'enabled' and Anonymous Authentication set to 'disabled'?
Are you certain that your Windows AD account is set up within Portal to begin with? To verify, go to Portal with either your initial administrator account or your own AD account and click on My Organization to see if your AD account got set up. The AD accounts get added to Portal upon the first initial login request from an AD account.
Try EMO again to see if it works under these conditions.
