Readonly database MDF file. Windows app

can someone help me.

I've tried moving the MDF file around to different locations but I'm still unable to update the database. I'm using Windows 7.

Here's my code:

using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace TestDatabase
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        System.Data.SqlClient.SqlConnection con;
        DataSet ds1;
        System.Data.SqlClient.SqlDataAdapter da;

        int MaxRows = 0;
        int inc = 0;

        private void Form1_Load(object sender, EventArgs e)
        {
            con = new System.Data.SqlClient.SqlConnection();
            ds1 = new DataSet();
            con.ConnectionString = "Data Source=.\\SQLEXPRESS;AttachDbFilename=C:\\Users\\rebdog\\AppData\\MyWorkers.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True";
            con.Open();

            string sql = "SELECT * From tblWorkers";
            da = new System.Data.SqlClient.SqlDataAdapter(sql, con);

            MessageBox.Show("database Open");

            da.Fill(ds1, "Workers");
            NavigateRecords();
            MaxRows = ds1.Tables["Workers"].Rows.Count;

            con.Close();

            MessageBox.Show("database closed");
        }

        private void btnSave_Click(object sender, EventArgs e)
        {
            System.Data.SqlClient.SqlCommandBuilder cb;

            cb = new System.Data.SqlClient.SqlCommandBuilder(da);

            DataRow dRow = ds1.Tables["Workers"].NewRow();

            dRow[1] = textBox1.Text;
            dRow[2] = textBox2.Text;
            dRow[3] = textBox3.Text;

            ds1.Tables["Workers"].Rows.Add(dRow);

            MaxRows = MaxRows + 1;
            inc = MaxRows - 1;

            da.Update(ds1,"Workers");
        }
    }
}

The code is from a tutorial, I need to get this working before I add a database to my project.

Thank you guys.