Permissions Help Needed

I am an administrator on my own local box and am trying to access IIS
locally (not over the network).

If I goto my web app using http://localhost it works fine

If I goto my web app using http://machinename or http://127.0.0.1 or
http://TheValidIPAddress I get:

401.1 Access is denied due to invalid credentails. Any advice or pointers
to articles would be appreciated. Thanks.