请问.net模拟POST的问题

从网上看到例子,如下System.Net.WebClient WebClientObj = new System.Net.WebClient();
   System.Collections.Specialized.NameValueCollection PostVars  = new System.Collections.Specialized.NameValueCollection();
   PostVars.Add("A1","0");
   PostVars.Add("A2","0");
   PostVars.Add("A3","000"); 
   try
   {
    byte[] byRemoteInfo   = WebClientObj.UploadValues("http://www.lovezhao.com/vote.asp","POST",PostVars);
    //下面都没用啦，就上面一句话就可以了
    string sRemoteInfo   = System.Text.Encoding.Default.GetString(byRemoteInfo);  
    //这是获取返回信息
    richTextBox_instr.Text  += sRemoteInfo;
   }
   catch
   {}测试后正常,但是把"http://www.lovezhao.com/vote.asp"改成"http://www.lovezhao.com/vote.asp?act=save"后总是有异常,请问怎么处理这种情况?