Unable to retrieve login errors

Hi.  

I have a basic login that creates a cookie if the credientials are fine.  Ideally, the credentials should be checked against my stored procedure. My problem is that if the user enters invalid information, an error message is not visible.  Can you tell me where I am erroring in my code below?  The work occurs in the login button click:

protected void LoginBtn_Click(object sender, EventArgs e)
    {
    //check username, password, and status (is user active)
        string username = Convert.ToString(usernm.Text);
        string password = Convert.ToString(passwordTxt.Text);

        string showUsers = ConfigurationManager.ConnectionStrings["RevisedTapeLibrary"].ConnectionString;
        SqlConnection conn = new SqlConnection(showUsers);

        SqlCommand comm = new SqlCommand("usp_LookupUserTG", conn);        

        comm.Connection.Open();
        comm.CommandType = CommandType.StoredProcedure;
        comm.Parameters.AddWithValue("@user", usernm.Text);
        comm.Parameters.AddWithValue("@passwd", passwordTxt.Text);

        comm.ExecuteNonQuery();

        SqlDataReader myreader = comm.ExecuteReader();

        if (myreader.HasRows)
        {
            while (myreader.Read())
            {
                string userrecord = Convert.ToString(myreader["UserID"]);
                int numValue = (int)myreader["TypeID"];

                string myEmail;
                if (myreader["email"] != DBNull.Value)
                {myEmail = (string)myreader["email"]; }
                else
                {myEmail = "None Provided";}

                string usertype = (string)myreader["UserType"];
                bool activeUser = (bool)myreader["active"];
                string pw = (string)myreader["Password"];
                string usercred = (string)myreader["Username"];

                if (usernm.Text != usercred || passwordTxt.Text != pw)
                {
                    Response.Write("Invalid Credentials");
                }
                else
                {
                    Response.Redirect("/tl_functions/tapelibstart.htm");
               

                HttpCookie aCookie = new HttpCookie("checkUser");
                aCookie.Values["Site"] = "Tape Library Application";
                aCookie.Values["LastVisit"] = DateTime.Now.ToString();
                aCookie.Values["Username"] = usernm.Text;
                aCookie.Values["Email"] = myEmail;
                aCookie.Values["User Type"] = usertype;

                string newTypeID = Convert.ToString(numValue);
                aCookie.Values["My Type"] = newTypeID;
                aCookie.Values["UID"] = userrecord;

                Response.SetCookie(aCookie);
                }
            }
        }
        comm.Connection.Close();

    }