I struggled also. I found you need to enter your Internet address for the username. Also you will need to enable SSL with DIIOP and start the HTTP task.
I had the same issue with the login. All I did was added the server fully qualified domain name to the DIIOP section of the Server doc (Internet Protocols-->DIIOP-->Host name/address) Then rebooted.
Make sure all DIIOP and HTTP Domino tasks are started after reboot.
I hope this helps!