I wrote this code but when I click on my save button. Its stack and show message that saying: instance failure. I do check the database path its sound correct. Its showing the but on conn.open;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;
namespace ElSoft_FactuStocks
{
    public partial class Facturacao : Form
    {
public Facturacao()
        {
            InitializeComponent();
            bindCombo();
        }
        SqlConnection conn;
        SqlCommand comm;
        SqlDataReader dreader;
        string connstr = @"Data Source=localhost\\sqlexpress;Initial Catalog=lunaoffice;Integrated Security=True";
private void btnGravar_Facturacao_Click(object sender, EventArgs e)
        {          
            conn = new SqlConnection(connstr);
            conn.Open();// here
comm = new SqlCommand("insert into fact values(" + symb.Text + ",'" + nomeClienteFactu.Text + ",'" + artigoFactu.Text + "'," + leituraCodFactu.Text +
 ",'" + quantidadeFactu.Text + ",'" + precosaidaFactu.Text + ",'" + totalFactu.Text + ",'" + descontoFactu.Text + ",'" + utilizadores.Text + "')", conn);
            try
                
                {
                    comm.ExecuteNonQuery();
                MessageBox.Show("Saved...");
                }
            catch (Exception)
                { 
                MessageBox.Show("Not Saved");
                }
            finally
                {
                conn.Close();
            }
}