Bad http connection (400) from Simple Native Iphone App to test .net Web Service

I have written a simple hello world .net web service which will accept 2 parameters and return the parameters as a string. The web service is hosted by IIS on a windows xp pc.

I am able to access the web service using safari on the iphone simulator, successfully tested the operation using HTTP POST by clicking the "invoke" button.

However, when I use the native app on the iphone simulator, I keep getting a bad http connection error 400 on the IIS log. I have tested my native app with http://viium.com/WebService/HelloWorld.asmx and it works.

I have already added

Does anyone know what is wrong? Is it some settings that have not configured correctly?

Thank you very much in advance.

400 has a special meaning for SOAP communication (aka classic ASP.NET web service, *.asmx)

http://www.w3.org/TR/soap12-part2/#http-bindrespnode

http://blogs.msdn.com/asiatech/archive/2009/06/12/http-head-requests-get-405-http-error-when-access-soap-web-services.aspx