调试易

private void btnLogin_Click(object sender, EventArgs e)
        {
            //读注册表 
            RegistryKey   regRead;
            //读取HKEY_CURRENT_USER主键里的Software子键下名为“Test”的子键
            regRead=   Registry.CurrentUser.OpenSubKey( "Software\\login ",true);
            if(regRead==null)   //如果该子键不存在 
            {
                MessageBox.Show("没有保存账号！");
            } 
            else 
            {                
                HtmlElement btnSubmit = webBrowser1.Document.All["staticsubmitid"];
                HtmlElement tbUserid = webBrowser1.Document.All["staticusernameid"];
                HtmlElement tbPasswd = webBrowser1.Document.All["staticpasswordid"];               
                if (tbUserid == null || tbPasswd == null || btnSubmit == null)
                    return;
                object nameobj = regRead.GetValue("name");     //读取“Name”项的值
                object passobj = regRead.GetValue("pass");     //读取“Name”项的值
                //label6.Text = nameobj.ToString();
                tbUserid.SetAttribute("string",nameobj.ToString());
                tbPasswd.SetAttribute("value",passobj.ToString());
                btnSubmit.InvokeMember("Click");                
            }
            //关闭该对象
            regRead.Close();
        }          
总是提示 
   {"未将对象引用设置到对象的实例。"}
这是为什么？
如果改为 tbUserid.SetAttribute("string",(string)nameobj);
                tbPasswd.SetAttribute("value",(string)passobj);
获取到的是空值。