没法模拟post数据

无法模拟post数据
http://www.phil-jobnet.dole.gov.ph/Hot.aspx

这个是我要抓取数据的页面，我想实现翻页，这个翻页是个post动作，但我模拟post 一直跳到错误页


 string ctl00_ToolkitScriptManager1_HiddenField = string.Empty;
                    string regex = "<script src=\"CombineScriptsHandler.ashx\\?_TSM_HiddenField_=ctl00_ToolkitScriptManager1_HiddenField&amp;_TSM_CombinedScripts_=([^\"]+)\" type=\"text/javascript\"></script>";
                    MatchCollection regexMatches = Regex.Matches(sHtml, regex, RegexOptions.Singleline | RegexOptions.IgnoreCase);
                    if (regexMatches != null && regexMatches.Count > 0)
                    {
                        ctl00_ToolkitScriptManager1_HiddenField =  regexMatches[0].Groups[1].Value.Trim();
                        ctl00_ToolkitScriptManager1_HiddenField = System.Web.HttpUtility.UrlDecode(ctl00_ToolkitScriptManager1_HiddenField);
                    }
                    string postdata = "ctl00$ToolkitScriptManager1=" + "ctl00$RightContents$upPnl1|ctl00$RightContents$Pager2$dlPages"+Environment.NewLine
                         + "&ctl00_ToolkitScriptManager1_HiddenField=" + ctl00_ToolkitScriptManager1_HiddenField + Environment.NewLine
                         + "&ctl00_RightContents_TabContainer1_ClientState=" + getcontroldata("ctl00_RightContents_TabContainer1_ClientState") + Environment.NewLine
                         + "&ctl00$RightContents$Pager2$dlPages=" + (iPageNo - 1).ToString() + Environment.NewLine
                         + "&ctl00$RightContents$Pager2$hfCurrentPage=1" + Environment.NewLine
                         + "&ctl00$RightContents$Pager2$hfPageSize=10" + Environment.NewLine
                         + "&ctl00$RightContents$Pager2$hfRowCount=" + getcontroldata("ctl00_RightContents_Pager2_hfRowCount") + Environment.NewLine
                         + "&ctl00$RightContents$Pager2$hfGoToLastPage=" + "False" + Environment.NewLine
                         + "&__EVENTTARGET=" + "ctl00$RightContents$Pager2$dlPages" + Environment.NewLine
                         + "&__EVENTARGUMENT=" + Environment.NewLine
                         + "&__LASTFOCUS=" + Environment.NewLine
                         + "&__VIEWSTATE=" + getcontroldata("__VIEWSTATE") + Environment.NewLine
                         + "&__EVENTVALIDATION=" + getcontroldata("__EVENTVALIDATION")+Environment.NewLine
                         + "&__ASYNCPOST=true";
                  

                    sHtml = post(postdata,sCurrentUrl);


post 方法：


   public string post(string postData, string uriStr)
        {
            string html = string.Empty;