probleme ajouter des donnees a une base de donnees sql server 2008

le code
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using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
 
namespace connection3
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
 
        private void button1_Click(object sender, EventArgs e)
        {
            string id = textBox1.Text.Trim();
            string nom = textBox2.Text.Trim();
            string prenom = textBox3.Text.Trim();
            string age = textBox4.Text.Trim();
            string connectionString = "connection3.Properties.Settings.testConnectionString";
            string requete = "INSERT INTO table_utulisateurs VALUES(id,nom,prenom,age)";
            using (SqlConnection connexion = new SqlConnection(connectionString))
            {
                connexion.Open();
                using (SqlCommand cmd = new SqlCommand(requete, connexion))
                {
                    cmd.Parameters.Add(new SqlParameter("@id", id));
                    cmd.Parameters.Add(new SqlParameter("@nom", nom));
                    cmd.Parameters.Add(new SqlParameter("@prenom", prenom));
                    cmd.Parameters.Add(new SqlParameter("@age", age));
 
                    cmd.ExecuteNonQuery();
                }
 
            }
        }
 
        private void Form1_Load(object sender, EventArgs e)
        {
 
        }
    }
}
aidez moi svp