Why POST data didn't work with my ASP.NET website

Since a week i try to contact my web server from a c++ application.

When i send a GET request, my server return the content of the webpage as expected, i also put a breakpoint to be sure it's loading the page in the Sub Page_Load.

Then i tryed to send POST request using WinHttpRequest. My server didn't receive any data. I'm using the WinHttpClient from here : codeproject.com WinHttpClient

I can provide futher details if needed.

If anyone have an idea, it would help a lot. Thanks