Enable SSL for web proxy

I have been told to setup an ISA 2004 as a web proxy for my company.
The goal is to use the ISA box to proxy both 80 and 443 traffic, as
well as to have users authenticate first. However, client machine
connections to the proxy need to be encrypted via SSL, but can then be
unencrypted from the ISA box out to the Internet. In other words, when
a user needs to browse the web, their browser needs to connect to the
proxy (ISA box) via SSL. Upon doing so, the user is challenged for
authentication. Post authentication, the ISA box proxies the web
traffic, unencrypted, out to the Internet. The reason the client
computer connections to the proxy must be encrypted is because clear
text, "Basic" authentication will be configured on the ISA server, but
there is no reason traffic from the proxy to the Internet needs to be
encrypted.

What I have done so far is under Networks, right click "Internal" to
open the "Properties" window. On the "Web Proxy" Tab, I have checked
"Enable HTTP...HTTP port 80". I also have enabled "Basic Authentication"
via the "Authentication" button. In my attempt to secure the proxy
connections to the ISA server, I checked the "Enable SSL" box, have
specified "SSL port 443", and for the "Certificate" box, I click the
"Select" button, but receive this error: "There are no certificates
configured on this server." Because this is just my test box, I have
the ISA server a CA, and have issued a Certificate.

Why is the cert I created not being seen? I need help setting up this
last piece...encrypting the traffic from the proxy clients to the proxy
server?

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