... forbidden with client authentication scheme Anonymous

[mzarlenga]

I have a client / server written in C#/VS2005 that uses WCF. Each
component exposes a secure (https endpoint with WCF. httpcfg was
used to secure the ports with certificates. (Both system use the same
certificate for their endpoints, in case that matters)

The client and server are on different physical systems.

The applications communicate like so:
Request: Client -----> Server's endpoint ( https://172.16.26.30:8283/MyServer
)
Response: Server -----> Client's endpoint ( https://172.16.26.31:40201/MyClient
)

The client works on every system I've tried it ... but one. On that
one system, when the Server tries to respond, the error the server
gets is: The HTTP request was forbidden with client authentication
scheme 'Anonymous'

This appears to be some kind of IIS setup issue on that one client
system.

I believe I've made sure that Anonymous access is enabled: Control
Panel > Administrative Tools > Internet Information Services > Web
Services > right click > Properties > Directory Security >
Authentication and Access Control > Enable Anonymous Access is
checked.

What else could be wrong? What am I missing?

Help!