WCF service fails to call another WCF service on same machine

WCF service fails to call another WCF service on same machine

I have a website hosted in IIS7 in server A. The website calls a web
service that is also hosted in server A, but the call returns an error
401. I tried referencing to the web service by IP address, host
(A.domain.com), and fully qualified dsn. None worked.
After some research, I found out about the loopback check, and the
BackConnectionHostNames.
Refer to this article
Disabling the loopback check fixes the problem, but is not a desirable
solution.
For the BackConnectionHostNames, I tried adding:
A
A.domain.com
A.full.domain.com
But it didn't work.
I played some with IIS http bindings for the website, I tried adding
A.domain.com to the host name, and I also tried setting the IP, but still
got the same error.
Am I missing something? (I clearly am...) Where else should I be looking at?
Any help appreciated. Thanks