WebBrowser后退，重新填表，然后出错了，求救啊！！

procedure TForm1.BtnStartClick(Sender: TObject);
var
  str: string;
  i,j: longint;
begin
  i := 0;
  for i := 0 to ListBoxName.Items.Count - 1 do
  begin
    while WebBrowser.Busy do
      Delay(50);
    with WebBrowser do
    begin
      OleObject.document.all.Item('xuehao').value := ListBoxNum.Items.Strings[i];  //i=0 时正常，i=1时报错；
      OleObject.document.all.Item('zhenhao').value := ListBoxName.Items.Strings[i];
      OleObject.document.all.Item('submit_query').click;
    end;
   {此处省略N行} 
    try
      WebBrowser.GoBack;
    except
      on E: Exception do
      begin
        {此处省略N行} 
      end;
    end;
  end;
end;

错误代码：First chance exception at $756EB9BC. Exception class EAccessViolation with message 'Access violation at address 004B7E61 in module 'GetResult.exe'. Read of address 00000000'. Process GetResult.exe (11244)

WebBrowser打开的网页： http://cx.zjzs.net/pg.asp （验证码在程序启动时手动输入）


[解决办法]
直接IdHTTP模拟Get/Post才是王道