error in updating a database

Question

i am new to ado.net and i have am having a problem in updating a database.

whenever i run the program an exception is raised.

error:uninitialized string  

i have checked the connection string and every thing is fine .

i can navigate the records backward and forward

i can add data to the datased 

but when i try to update data into the database then this exception error arises.

i searched every where but unable to find any solution ...

following code...

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Windows.Forms;

namespace WindowsFormsApplication16

{

    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();

                //(@"Data Source=\SQLEXPRESS;AttachDbFilename=F:\MyWorkers1.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True");

            con.ConnectionString = "Data Source=\\SQLEXPRESS;AttachDbFilename=F:\\MyWorkers1.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True";

            

            ds1 = new DataSet();

           

            string sql = "SELECT * from tblWorkers";

            da =new System.Data.SqlClient.SqlDataAdapter(sql, con);

            con.Open();

            da.Fill(ds1, "Workers");

            NavigateRecords();

            MaxRows = ds1.Tables["Workers"].Rows.Count;

            MessageBox.Show("open");

            con.Close();

            MessageBox.Show("close");

            con.Dispose();

        }

        private void NavigateRecords()

        {

            DataRow dRow = ds1.Tables["Workers"].Rows[inc];//dataset me jo data rakha hay wo 

            //text boxes medaldo

            textBox1.Text = dRow.ItemArray.GetValue(1).ToString();

            textBox2.Text = dRow.ItemArray.GetValue(2).ToString();

            textBox3.Text = dRow.ItemArray.GetValue(3).ToString();

        }

        private void button1_Click(object sender, EventArgs e)

        {

            if (inc != MaxRows - 1)

            {

                inc++;

                NavigateRecords();

            }

            else

            { MessageBox.Show("last record"); }

        }

        private void button2_Click(object sender, EventArgs e)

        {

            if (inc != 0)

            {

                inc--;

                NavigateRecords();

            }

            else { MessageBox.Show("first row"); }

        }

        private void button3_Click(object sender, EventArgs e)

        {

            if (inc != MaxRows - 1)

            { inc = MaxRows - 1;

            NavigateRecords();

            }

        }

        private void button4_Click(object sender, EventArgs e)

        {

            if (inc != 0)

            { inc = 0;

            NavigateRecords();

            }

        }

        private void button5_Click(object sender, EventArgs e)

        {

            textBox1.Clear();

            textBox2.Clear();

            textBox3.Clear();

        }

        private void button6_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");   //exception is raised on this line...

            MessageBox.Show("entery added into database");

        }

    }

}