How can I debug authentication issue in a local webservice method call?

I have an ASP .NET webpage which calls an ASP.NET webservice existing on the same site. Both of them require integrated windows authenticatio开发者_Python百科n.

I get the following error during invoke of the webservice method when I run my webpage: "The request failed with HTTP status 401: Unauthorized. "

I have no clue why it is failing. Is there a way to know which authentication protocol is being used from the website to invoke the webservice method, and why it is failing?

EDIT : As suggested, I downloaded auth diagnostics, and monitored it when i ran my webpage. Following is result:

AcceptSecurityContext Package=NTLM Result=0x0 ContextAttr=0x12001c UserName= ClientName= ServerName=Result=0x0(Fail: context has ASC_RET_NULL_SESSION flag) Main process: Finished, 1 issue detected

Have you gone through the Microsoft Troubleshooting HTTP 401 errors article?

How is IIS configured? Is it set up to use anonymous or Windows Auth? Also, what context is the app pool using? Perhaps the web is running under a context that doesn't have permissions to hit the web service?