A particular scenario of IIS security settings causes a problem with IE
browsers (v6 & v7) whereby no post data is sent to the server and the http
header content-length is set to 0.

To reproduce this behaviour, follow the steps below:

1) Create a web application with a default.aspx page containing a button
such as,
<asp:Button ID="testsubmit" runat="server" Text="test" />
2) Add the following code in the page_load event handler,
       if (this.IsPostBack)
           Response.Write("IsPostBack = true");
       else
           Response.Write("IsPostBack = false");
3) Set the home directory of the root website in iis6.0 to point to the
above web application.
4) Set the root website (i.e. localhost) to iis integrated windows
authentication.
5) Create a virtual directory below this (i.e. localhost/subdomain1) with
the home directory pointing to the same folder as the root.
6) Set the virutal directory (i.e. subdomain1) to iis anonymous access.
7) Create another virtual directory below the root (i.e.
localhost/subdomain2) with the home directory pointing to the same folder as
the root.
8) Set the virutal directory (i.e. subdomain2) to iis integrated windows
authentication. (we now have 3 identical web applications with one sub domain
configured to anonymous access whilst the other two set to windows integrated
authentication)
9) Open up IE v6 or v7.
10) Request the root website (i.e. localhost)
11) Submit form
12) Observe response value 'true'.
13) Request the virtual direcotry (i.e. localhost/subdomain1)
14) Submit form
15) Observe response value 'true'.
16) Request the virtual direcotry (i.e. localhost/subdomain2)
17) Submit form
18) Observe response value 'false'.
19) Repeat steps 9-17 with Firefox v2.

Conclusion

Content-length set to 0 by IE, no post data sent
This behaviour can not be reproduced in Firefox v2.

Any ideas why this ocurrs in IE?