在winform中用httpwebrequest表单post登录失败。

在winform中用httpwebrequest表单post登录失败。报错：远程服务器返回错误: (500) 内部服务器错误。
为什么会这样呢？
-----------------------------------------以下是winform代码----------------------------------------
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using the_n = System.Net;
using the_en = System.Text;
using System.IO;
using System.Net;namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }        private void Form1_Load(object sender, EventArgs e)
        {        }        private void button1_Click(object sender, EventArgs e)
        {            try
            {
                the_n.HttpWebRequest hwr = (the_n.HttpWebRequest)the_n.HttpWebRequest.Create(@"http://www.nmec.org.cn/ViewScore/ViewScoreBS.aspx");
                long lo = 4417831100984;                string the_data = @"__VIEWSTATE=/wEPDwUIMjcyNTAxMDZkZDsl2K15D71MYrXXjTh5uDX7N0Bk" +
             @"&_EVENTVALIDATION=/wEWBQLZ76K7AwKu1/C5AgK047EHAqfj5cgLAvqc4c8EmQ1XrLWvzZ7O2XyE80W7uFla2Pg=" +
             @"&txtXINGMING=aaa" +
             @"&txtSFZH=440229192108042212" +
             @"&txtZKZH=" + lo +
             @"&__EVENTTARGET=" +
             @"&__EVENTARGUMENT=";
                          Encoding encoding = Encoding.GetEncoding("GB2312");   
                hwr.AllowAutoRedirect = true;                byte[] sendda = encoding.GetBytes(the_data);
                hwr.Method = "POST";
                hwr.ContentType = "application/x-www-form-urlencoded";
                hwr.ContentLength = sendda.Length;
                System.IO.Stream newStream = hwr.GetRequestStream();
                newStream.Write(sendda, 0, sendda.Length);
                newStream.Close();
                HttpWebResponse myResponse = (HttpWebResponse)hwr.GetResponse();
                StreamReader reader = new StreamReader(myResponse.GetResponseStream(), Encoding.GetEncoding("GB2312"));
                string content = reader.ReadToEnd();
                this.textBox1.Text = content;            }
            catch (Exception eee)
            {
                this.textBox1.Text = eee.Message.ToString();            }        }
    }
}--------------------------------------------------------以下是要求登录的HTML页面：----------------------------------------------------<!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 id="Head1"><title>
2009年医师资格考试医学综合笔试成绩查询
</title><link href="css/style.css" rel="Stylesheet" /></head>
<body>
    <form name="form1" method="post" action="ViewScoreBS.aspx" onsubmit="javascript:return WebForm_OnSubmit();" id="form1">
<div>
<input type="hidden" name="__EVENTTARGET" id="__EVENTTARGET" value="" />
<input type="hidden" name="__EVENTARGUMENT" id="__EVENTARGUMENT" value="" />
<input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE" value="/wEPDwUIMjcyNTAxMDZkZDsl2K15D71MYrXXjTh5uDX7N0Bk" />
</div><script type="text/javascript">
//<![CDATA[
var theForm = document.forms['form1'];
if (!theForm) {
    theForm = document.form1;
}
function __doPostBack(eventTarget, eventArgument) {
    if (!theForm.onsubmit || (theForm.onsubmit() != false)) {
        theForm.__EVENTTARGET.value = eventTarget;
        theForm.__EVENTARGUMENT.value = eventArgument;
        theForm.submit();
    }
}
//]]>
</script>
<script src="/ViewScore/WebResource.axd?d=312VsCNNFSWmWCQVxRgcyQ2&amp;t=633595624183430636" type="text/javascript"></script>
<script src="/ViewScore/WebResource.axd?d=-OjobeIKMlqzP4Jcj_jozcaC6bmEFixugIcT6QnfsgA1&amp;t=633595624183430636" type="text/javascript"></script>
<script type="text/javascript">
//<![CDATA[
function WebForm_OnSubmit() {
if (typeof(ValidatorOnSubmit) == "function" && ValidatorOnSubmit() == false) return false;
return true;
}
//]]>
</script><div> <input type="hidden" name="__EVENTVALIDATION" id="__EVENTVALIDATION" value="/wEWBQLZ76K7AwKu1/C5AgK047EHAqfj5cgLAvqc4c8EmQ1XrLWvzZ7O2XyE80W7uFla2Pg=" />
</div>
    <table cellspacing="0" id="tblMain">
        <tr>
            <td valign="top" style="height: 100px;">
                <img src="images/head1.gif" alt="" />
            </td>
        </tr>
        <tr>
            <td style="height: 7px; background: url(images/menu.gif);">
            </td>
        </tr>
        <tr>
            <td height="12" style="background: url(images/shadow.gif)">
            </td>
        </tr>
        <tr>
            <td align="center" style="background-color: #FFFFFF">
                <br />
                <table width="700" style="background-color: #F6F6F6">
                    <tr>
                        <td class="blacktitle">
                            <br />
                            2009年医师资格考试医学综合笔试成绩查询
                            <hr size="1" style="color: #C5C5C5" />
                            
                        </td>
                    </tr>
                    <tr>
                        <td>
                            <table id="divShowBody" width="100%">
<tr>
<td class="label">
                                        姓名：
                                    </td>
<td class="content">
                                        <input name="txtXINGMING" type="text" id="txtXINGMING" class="WenBen" />
                                    </td>
<td align="left">
                                        <span id="valrXINGMING" style="color:Red;display:none;"> 请填写姓名</span>
                                    </td>
</tr>
<tr>
<td class="label">
                                        身份证号：
                                    </td>
<td class="content">
                                        <input name="txtSFZH" type="text" id="txtSFZH" class="WenBen" />
                                    </td>
<td align="left">
                                        <span id="valrSFZH" style="color:Red;display:none;"> 请填写证件编号</span>
                                    </td>
</tr>
<tr>
<td class="label">
                                        准考证号：
                                    </td>
<td class="content">
                                        <input name="txtZKZH" type="text" id="txtZKZH" class="WenBen" />
                                    </td>
<td align="left">
                                        <span id="valrZKZH" style="color:Red;display:none;"> 请填写笔试准考证号</span>
                                    </td>
</tr>
<tr>
<td colspan="3" align="center">
                                        <br />
                                        <input type="submit" name="btnView" value="查  询" onclick="javascript:WebForm_DoPostBackWithOptions(new WebForm_PostBackOptions(&quot;btnView&quot;, &quot;&quot;, true, &quot;&quot;, &quot;&quot;, false, false))" id="btnView" />
                                    </td>
</tr>
</table>                        </td>
                    </tr>
                    <tr>
                        <td>
                            
                        </td>
                    </tr>
                </table>
                <br />
                <br />
                <input type="submit" value="关闭窗口" onclick="window.close();return false;" />
                <br />
                <br />
            </td>
        </tr>
        <tr>
            <td height="10" style="background: url(images/footer.gif)">
            </td>
        </tr>
        <tr>
            <td>
                <div id="foot1">
                    国家医学考试中心 版权所有&nbsp; <a href="http://www.miibeian.gov.cn" target="_blank" title="中华人民共和国信息产业部ICP/IP地址信息备案号"
                        class="White">京ICP备07005584号</a>
                </div>
            </td>
        </tr>
    </table>
    
<script type="text/javascript">
//<![CDATA[
var Page_Validators =  new Array(document.getElementById("valrXINGMING"), document.getElementById("valrSFZH"), document.getElementById("valrZKZH"));
//]]>
</script><script type="text/javascript">
//<![CDATA[
var valrXINGMING = document.all ? document.all["valrXINGMING"] : document.getElementById("valrXINGMING");
valrXINGMING.controltovalidate = "txtXINGMING";
valrXINGMING.focusOnError = "t";
valrXINGMING.errormessage = " 请填写姓名";
valrXINGMING.display = "Dynamic";
valrXINGMING.evaluationfunction = "RequiredFieldValidatorEvaluateIsValid";
valrXINGMING.initialvalue = "";
var valrSFZH = document.all ? document.all["valrSFZH"] : document.getElementById("valrSFZH");
valrSFZH.controltovalidate = "txtSFZH";
valrSFZH.focusOnError = "t";
valrSFZH.errormessage = " 请填写证件编号";
valrSFZH.display = "Dynamic";
valrSFZH.evaluationfunction = "RequiredFieldValidatorEvaluateIsValid";
valrSFZH.initialvalue = "";
var valrZKZH = document.all ? document.all["valrZKZH"] : document.getElementById("valrZKZH");
valrZKZH.controltovalidate = "txtZKZH";
valrZKZH.focusOnError = "t";
valrZKZH.errormessage = " 请填写笔试准考证号";
valrZKZH.display = "Dynamic";
valrZKZH.evaluationfunction = "RequiredFieldValidatorEvaluateIsValid";
valrZKZH.initialvalue = "";
//]]>
</script>
<script type="text/javascript">
//<![CDATA[var Page_ValidationActive = false;
if (typeof(ValidatorOnLoad) == "function") {
    ValidatorOnLoad();
}function ValidatorOnSubmit() {
    if (Page_ValidationActive) {
        return ValidatorCommonOnSubmit();
    }
    else {
        return true;
    }
}
        //]]>
</script>
</form>
</body>
</html>