What causes the WCF service/server to expect 'Negotiate,NTLM'?

I realize there are lots of proposed solutions to the problem of "The HTTP request is unauthorized with client authentication scheme 'Negotiate'. The authentication header received from the server was 'Negotiate,NTLM'" but none have worked for me. I believe the error I continue to receive is related to the IIS configuration but I can't be positive.

That said, I'd like to understand why I receive this message. I can read a开发者_开发技巧 three line solution as well as anyone but when they don't work it puts me at a loss. What is causing the server to expect 'Negotiate,NTLM'? Is this something I should/can change? Why is the client sending only 'Negotiate' ? Are these web.config related items only? I appreciate any information you can provide that would help me ask more intelligent questions and search for more relevant answers. Thanks!

NTLM authentication is Windows authentication over HTTP. The Negotiate indicates to either use kerberos (ActiveDirectory) when it is available or NTLM if not. A brief overview is at MSDN article. In IIS, setting the web site to allow Windows authentication is required to enable the Negotiate,NTLM setting.