DefaultCrendentials not working

[Rich]

I have an aspx page which uses a WebRequest object to post some XML to
a standard asp page. Both the aspx and asp pages require NT
autentication. I have added:

<location path="secure">
<system.web>
<authorization>
<deny users="?" />
</authorization>
</system.web>
</location>

To the web.config file for the aspx page and have set IIS to require
NT authentication (with anonymous access turned off) on both the aspx
web application and the asp web site.

When I do the post from the aspx page I set the Credentials for the
WebRequest object to CredentialCache.DefaultCredentials.

I call the aspx page from a cleint app running under a domain account.
If I place the aspx page and the asp page on different physical
machines everything is fine. However, if I put the asp and aspx
applications on the same machine (running under the same instance of
IIS) I start experiencing problems.

Any ideas?

Regards

Rich