i get this error when i run The Process cannot access the file because it is used by another process.

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Drawing;

using System.Text;

using System.Windows.Forms;

using System.Data.SqlClient;

namespace Pay_Roll_Applications

{

    public partial class Form2 : Form

    {

        SqlConnection con = new SqlConnection("Server=(local);initial catalog=Payroll;Trusted_Connection=True");

        public Form2()

        {

            InitializeComponent();

        }

        private void Form2_Load(object sender, EventArgs e)

        {

            int i;

            for (i = 1; i <= 31; i++)

            {

                comboBox1.Items.Add(i);

            }

            txt_basicscale.Text = "0";

            txt_hrascale.Text = "0";

            txt_dascale.Text = "0";

            txt_variablescale.Text = "0";

            txt_working.Text = "31";

            txt_basicamount.Text = "0";

            txt_hraamt.Text = "0";

            txt_daamt.Text = "0";

            txt_variableamt.Text = "0";

        }

        private void button3_Click(object sender, EventArgs e)

        {

            con.Open();

            SqlCommand cmd = new SqlCommand("insert into pay values('" + cb_id.Text + "'," + txt_working.Text + ",' " + txt_Name.Text + "','" + txt_fathers.Text + "','" + txt_pan.Text + "','" + txt_date.Text + "'," + txt_days.Text + ",'" + txt_branch.Text + "',' " + txt_designation.Text + "','" + txt_department.Text + "',' " + txt_pay.Text + "','" + txt_bankname.Text + "'," + txt_accno.Text + "," + txt_basicamount.Text + "," + txt_hraamt.Text + "," + txt_daamt.Text + ", " + txt_variableamt.Text + "," + txt_percentagebasic.Text + "," + txt_excessmobile.Text + "," + txt_tds.Text + "," + txt_loan.Text + "," + txt_netpay.Text + ")", con);

            cmd.ExecuteNonQuery();

        }

        private void cb_id_SelectedIndexChanged(object sender, EventArgs e)

        {

            con.Open();

            SqlCommand cmd1 = new SqlCommand("select * from pay where Employeeid = '" + cb_id.Text + "'", con);

            SqlDataReader dr = cmd1.ExecuteReader();

            while (dr.Read())

            {

                txt_Name.Text = dr[2].ToString().Trim();

                txt_fathers.Text = dr[3].ToString().Trim();

                txt_pan.Text = dr[4].ToString().Trim();

                txt_date.Text = dr[5].ToString().Trim();

                txt_branch.Text = dr[7].ToString().Trim();

                txt_designation.Text = dr[8].ToString().Trim();

                txt_department.Text = dr[9].ToString().Trim();

                txt_pay.Text = dr[10].ToString().Trim();

                txt_bankname.Text = dr[11].ToString().Trim();

                txt_accno.Text = dr[12].ToString().Trim();

                txt_basicscale.Text = dr[13].ToString().Trim();

                txt_hrascale.Text = dr[14].ToString().Trim();

                txt_dascale.Text = dr[15].ToString().Trim();

                txt_variablescale.Text = dr[16].ToString().Trim();

                txt_excessmobile.Text = dr[18].ToString().Trim();

                txt_tds.Text = dr[19].ToString().Trim();

                txt_loan.Text = dr[20].ToString().Trim();

                txt_basicamount.Text = "";

                txt_hraamt.Text = "";

                txt_daamt.Text = "";

                txt_variableamt.Text = "";

                txt_scaletot.Text = "";

                txt_amttot.Text = "";

                textBox1.Text = "";

                txt_netpay.Text = "";

                txt_days.Text = "";

                txt_percentagebasic.Text = "";

            }

            con.Close();

            con.Open();

            SqlCommand cmd2 = new SqlCommand("select * from pay where Employeeid='" + cb_id.Text + "'", con);

            SqlDataReader dr1 = cmd2.ExecuteReader();

            while (dr1.Read())

            {

                txt_percentagebasic.Text = dr1[17].ToString().Trim();

            }

            con.Close();

            //con.Open();

            //SqlCommand cmd3 = new SqlCommand("select * from vt where id='" + cb_id.Text + "'", con);

            //SqlDataReader dr2 = cmd3.ExecuteReader();

            //while (dr2.Read())

            //{

            //    txt_excessmobile.Text = dr2[6].ToString().Trim();

            //    txt_tds.Text = dr2[5].ToString().Trim();

            //    txt_loan.Text = dr2[4].ToString().Trim();

            //}

            //con.Close();

            

        }

        private void button5_Click(object sender, EventArgs e)

        {

            Form1 f1 = new Form1();

            f1.Show();

            this.Hide();

        }

        private void dateTimePicker1_ValueChanged(object sender, EventArgs e)

        {

            DateTime dt = dateTimePicker1.Value;

            int days = DateTime.DaysInMonth(dt.Year, dt.Month);

            txt_working.Text = days.ToString();

            //int r, d1;

            //r = Convert.ToInt32(txt_variablescale.Text);

            //d1 = Convert.ToInt32(1 * r);

            //txt_variableamt.Text = d1.ToString();

            //txt_variableamt.Text = "0";

        }

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)

        {

            txt_days.Text = comboBox1.Text;

            int r, d1;

            r = Convert.ToInt32(txt_variablescale.Text);

            d1 = Convert.ToInt32(1 * r);

            txt_variableamt.Text = d1.ToString();

            int c, d;

            c = Convert.ToInt32(txt_basicscale.Text);

            d = Convert.ToInt32(0.12 * c);

            txt_percentagebasic.Text = d.ToString();

            double working_days = Convert.ToDouble(txt_working.Text);

            double payable_days = Convert.ToDouble(txt_days.Text);

            double a = Convert.ToDouble(txt_basicscale.Text);

            txt_basicamount.Text = Math.Floor(a / working_days * payable_days).ToString();

            double working_days1 = Convert.ToDouble(txt_working.Text);

            double payable_days1 = Convert.ToDouble(txt_days.Text);

            double a1 = Convert.ToDouble(txt_hrascale.Text);

            txt_hraamt.Text = Math.Floor(a1 / working_days1 * payable_days1).ToString();

            double working_days2 = Convert.ToDouble(txt_working.Text);

            double payable_days2 = Convert.ToDouble(txt_days.Text);

            double a2 = Convert.ToDouble(txt_dascale.Text);

            txt_daamt.Text = Math.Floor(a2 / working_days2 * payable_days2).ToString();

            double working_days3 = Convert.ToDouble(txt_working.Text);

            double payable_days3 = Convert.ToDouble(txt_days.Text);

            double a3 = Convert.ToDouble(txt_variablescale.Text);

            txt_variableamt.Text = Math.Floor(a3 / working_days3 * payable_days3).ToString();

            txt_amttot.Text = "";

            textBox1.Text = "";

            txt_netpay.Text = "";

        }

        private void button1_Click(object sender, EventArgs e)

        {

            double BasicScale, HraScale, DaScale, VpiScale, BasicAmt, Hraamt, daAmt, VpiAmt, PercentBasic, Excess, Tds, Loan, total, total1, total2, total3, total4;

            BasicScale = Convert.ToDouble(txt_basicscale.Text);

            HraScale = Convert.ToDouble(txt_hrascale.Text);

            DaScale = Convert.ToDouble(txt_dascale.Text);

            VpiScale = Convert.ToDouble(txt_variablescale.Text);

            BasicAmt = Convert.ToDouble(txt_basicamount.Text);

            Hraamt = Convert.ToDouble(txt_hraamt.Text);

            daAmt = Convert.ToDouble(txt_daamt.Text);

            VpiAmt = Convert.ToDouble(txt_variableamt.Text);

            PercentBasic = Convert.ToDouble(txt_percentagebasic.Text);

            Excess = Convert.ToDouble(txt_excessmobile.Text);

            Tds = Convert.ToDouble(txt_tds.Text);

            Loan = Convert.ToDouble(txt_loan.Text);

            total = BasicScale + HraScale + DaScale + VpiScale;

            txt_scaletot.Text = total.ToString();

            total1 = BasicAmt + Hraamt + daAmt + VpiAmt;

            txt_amttot.Text = total1.ToString();

            total2 = PercentBasic + Excess + Tds + Loan;

            textBox1.Text = total2.ToString();

            int a, b, c;

            if (!int.TryParse(txt_amttot.Text, out a) || a < 0)

            {

                txt_amttot.Focus();

                return;

            }

            if (!int.TryParse(textBox1.Text, out b) || b < 0)

            {

                textBox1.Focus();

                return;

            }

            c = a - b;

            txt_netpay.Text = c.ToString();

        }

    }

}