也许你必须检查，如果用户进行身份验证或没有，因为文本框里面的AnonymousTemplate或者它是一个命名空间的问题（ WebControls.Login ）

Maybe you must check if the user is authenticated or not, because the TextBox is inside the AnonymousTemplate or it's a Namespace issue(WebControls.Login):

if (!HttpContext.Current.User.Identity.IsAuthenticated) {
   Login lg = (WebControls.Login)LoginView1.FindControl("Login1");
   TextBox tb = (TextBox)lg.FindControl("UserName");
   Label2.Text = tb.Text;
}

但通常你会得到通过适当的属性，用户名/密码UserName/Password的登录。

修改：您的额外的截图是非常小的，但我看到你得到一个InvalidCastException，所以我对空间问题asumption是正确的。

Edit: Your added screenshot is very small but i see that you are getting an InvalidCastException, so my asumption on the namespace issue was correct.