HttpWebRequest Post的结果与在IE上点击POST的结果不一样，为什么？

该页面上的代码：
<form name="customerForm" method="post" action="/customer/setParameter.do" onsubmit="return validateForm(this) && !isGreaterThanToday();"><div><input type="hidden" name="org.apache.struts.taglib.html.TOKEN" value="1750e99c3269fce42bd87c3952484a4c"></div>
    交易日期
    <input type="text" name="tradeDate" maxlength="10" size="10" value="">
  <script language="JavaScript" type="text/javascript">
              document.forms["customerForm"].elements["tradeDate"].value='2011-01-07';
              </script>
                  <script language="JavaScript" type="text/javascript">
              function fPopUpCalendarDlg(ctrlobj)
              {
   showx = event.screenX - event.offsetX - 4 - 210 ; // + deltaX;
        showy = event.screenY - event.offsetY + 18; // + deltaY;
        newWINwidth = 210 + 4 + 18;
    var retval=window.open("/CalendarDlg.htm", "", "Width=185px, Height=250px,Left="+showx+"px, Top="+showy+"px"  );
         retval.obj=ctrlobj
}
                  </script>
    <IMG style="CURSOR: hand" 
                  onclick="fPopUpCalendarDlg(document.customerForm.tradeDate);return false" 
                  height=16  src="/img/calendar.gif" width=16 
                  align=absMiddle> 盈亏计算方式
    <select name="byType"><option value="date">逐日盯市</option><option value="trade">逐笔对冲</option></select>          <script language="JavaScript" type="text/javascript">
                    document.forms["customerForm"].elements["byType"].value='trade';
                  </script>
         
      <input type="submit" value="提交" class="button">         
</form>
对应这块代码，我执行HttpWebRequest Post 的代码如下：
            ASCIIEncoding encoding = new ASCIIEncoding();
            string postData = "tradeDate=" + dt.Year.ToString() + "-" + dt.Month.ToString() + "-" + dt.Day.ToString();
            postData += ("&byType=" + calculateKind);
            postData += ("&org.apache.struts.taglib.html.TOKEN=" + hideToken);            byte[] data = encoding.GetBytes(postData);            // Prepare web request...   
            HttpWebRequest myRequest =
                (HttpWebRequest)WebRequest.Create(domain + "/customer/setParameter.do");
            myRequest.UserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; .NET CLR 1.1.4322)";
            myRequest.Method = "POST";
            myRequest.ContentType = "application/x-www-form-urlencoded";
            myRequest.ContentLength = data.Length;            if (myRequest.CookieContainer == null)
            {
                myRequest.CookieContainer = new CookieContainer();
            }
            if (inputCC != null)
            {
                myRequest.CookieContainer.Add(inputCC);
            }
            Stream newStream = myRequest.GetRequestStream();            // Send the data.   
            newStream.Write(data, 0, data.Length);
            newStream.Close();            // Get response   
            HttpWebResponse myResponse = (HttpWebResponse)myRequest.GetResponse();             
            outputCC = myResponse.Cookies;            StreamReader reader = new StreamReader(myResponse.GetResponseStream(),  Encoding.UTF8);
            string content = reader.ReadToEnd();1. 结果我的代码反回空字符即 content为空。 而如果通过IE来点击"提交"按钮，则页面转到了其他页面上去。这是第一个问题？
2. 实际上上面的POST实际上是上传了参数到服务器中，为什么通过IE点击"提交"按钮能够成功的修改了参数，而我用HttpWebRequest 却不能成功修改？