Stored Procedure to textBox

 //!=======================================
        //!GETS ALL RECORDS FROM DATABASE==WORKING
        //!=======================================
        BindingSource binder = new BindingSource();
        private void btnGetAll_Click(object sender, EventArgs e)
        {
            string conString;
            conString = Properties.Settings.Default.jobsConnectionString;

            SqlConnection con;
            con = new SqlConnection(conString);

            con.Open();

            SqlCommand cmd;
            cmd = new SqlCommand("AllRecords", con);

            SqlDataAdapter adaptor;
            adaptor = new SqlDataAdapter(cmd);

            DataTable dataTable;
            dataTable = new DataTable();

            adaptor.Fill(dataTable);

            dataGridView1.DataSource = binder;

            binder.DataSource = dataTable;
            con.Close();
        }

        //!=========================================================
        //!ATTEMPT TO GET STORED PROCEDURE TO DISPLAY INTO A TEXTBOX
        //!=========================================================
        private void button1_Click(object sender, EventArgs e)
        {

            string conString;
            conString = Properties.Settings.Default.jobsConnectionString;

            SqlConnection con;
            con = new SqlConnection(conString);

            con.Open();

            SqlCommand cmd;
            cmd = new SqlCommand("SumTest", con);

            SqlDataAdapter adaptor;
            adaptor = new SqlDataAdapter(cmd);

            SqlDataReader reader;
            reader = cmd.ExecuteReader();
            while (reader.Read())
            {
                textBox1.Text = reader["SumTest"].ToString();
            }

            con.Close();
        }

RETURNS ERROR: System.IndexOutOfRangeException: 'SumTest'