Outlook RPC over HTTP

I am trying to make Exchange over HTTP work. I have gone through every TechNet articel I can find to set this thing up.

OWA already is set up and works fine. The few checks MS suggests to verify if RPC is working seem good.

Trouble is that I cannot get past the dialog box asking me to login to my domain. I can try to enter the user and password a million times and it will never fail or succeed.

It works fine when I am physically connected to the network.

Any ideas?