Sencha Touch Error You're trying to decode an invalid JSON String HTML page returns in ASP.NET

When I try to post JSON string to client side, I have the error below.

Uncaught Error: You're trying to decode an invalid JSON String: 

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head><title>

</title></head>
<body>
    <form method="post" action="WebForm1.aspx" id="form1">
<div class="aspNetHidden">
<input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE" value="/wEPDwULLTE2MTY2ODcyMjlkZDU/UqTLS4JCyWg8lH2WKg+TKxlfMLv46f+TlE5HbZ5k" />
</div>

    <div>

    </div>
    </form>
</body>
</html>

It returns all HTML page. My server side code is like this:

var httpWebRequest = (HttpWebRequest)WebRequest.Create("http://localhost:59145/My%20Application.app/webapp/index.html");
        httpWebRequest.ContentType = "application/json";
        httpWebRequest.Method = "POST";
        string json = "{ \"myresultlist\": [ {\"uname\": \"1\",\"pass\": \"anne\" }, { \"uname\": \"2\", \"pass\": \"jack\" }, {\"uname\": \"3\", \"pass\": \"Tom\" } ]}";


        httpWebRequest.ContentLength = json.Length;

        using (var streamWriter = new StreamWriter(httpWebRequest.GetRequestStream()))
        {

            streamWriter.Write(json);
            streamWriter.Flush();
            streamWriter.Close();

        }

Anybody has any idea? How can I send only JSON string to client?

Solution

The solution is below.

The reason for error is server side post operation.

When I change the code with this block, i get the json string.

Response.Expires = 0;
Response.ContentType = "application/json";
        Response.Write("{ \"myresultlist\": [ {\"uname\": \"1\",\"pass\": \"anne\" }, { \"uname\": \"2\", \"pass\": \"jack\" }, {\"uname\": \"3\", \"pass\": \"Tom\" } ]}");
        Response.End();