Dear Sir,
I want to avoid update duplicate Voucher No. while click on Settled button.
please sir help me.
namespace BPM
{
    public partial class vw : System.Web.UI.Page
    {
        int empno = 0;
        protected void Page_Load(object sender, EventArgs e)
        {
            empno = Convert.ToInt32(Request.QueryString["Id"].ToString());
            Session["EmpId"] = empno;
            String EmplooyeId = Session["emp_id"].ToString();
            Label12.Text = " " + EmplooyeId + "";
            String emp_nm = Session["emp_nm"].ToString();
            Label14.Text = "" + emp_nm + " ";
            String dept = Session["dept"].ToString();
            Label15.Text = "" + dept + " ";
            if (!IsPostBack)
            {
                BindTextBoxvalues();
                // BindGrid();
            }
            TextBox10.Visible = false;
            Button6.Visible = false;
            Button7.Visible = false;
            Label16.Text = String.Format("{0}", DateTime.Now.ToString("dd/MM/yyyy"));
        }
        private void BindTextBoxvalues()
        {
            string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
            SqlConnection con = new SqlConnection(constr);
            SqlCommand cmd = new SqlCommand("select * from bpms where Id=" + empno, con);
            DataTable dt = new DataTable();
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            da.Fill(dt);
            Label1.Text = dt.Rows[0][0].ToString();
            Label3.Text = dt.Rows[0][1].ToString();
            Label2.Text = dt.Rows[0][2].ToString();
            Label13.Text = dt.Rows[0][3].ToString();
            Label4.Text = dt.Rows[0][4].ToString();
            Label5.Text = dt.Rows[0][5].ToString();
            Label6.Text = dt.Rows[0][6].ToString();
            TextBox11.Text = dt.Rows[0][7].ToString();
            TextBox12.Text = dt.Rows[0][8].ToString();
            Label9.Text = dt.Rows[0][9].ToString();
            Label10.Text = dt.Rows[0][10].ToString();
            TextBox14.Text = dt.Rows[0][11].ToString();
            Label19.Text = dt.Rows[0][33].ToString();
        }
        protected void Button1_Click(object sender, EventArgs e)
        {            
            string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
            using (SqlConnection con = new SqlConnection(constr))
            {
                using (SqlCommand cmd1 = new SqlCommand("SELECT * FROM bpms WHERE vchr_no=@vchr_no", con))
                {
                    using (SqlDataAdapter da1 = new SqlDataAdapter(cmd1))
                    {
                        con.Open();
                        cmd1.Parameters.AddWithValue("@vchr_no", this.TextBox13.Text.Trim());
                        DataSet ds1 = new DataSet();
                        da1.Fill(ds1);
                        if (ds1.Tables[0].Rows.Count > 0)
                        {
                            string message = "Duplicate Voucher No. Number Not Allowed !!";
                            string script = "window.onload = function(){ alert('";
                            script += message;
                            script += "');";
                            script += "window.location = '";
                            script += Request.Url.AbsoluteUri;
                            script += "'; }";
                            ClientScript.RegisterStartupScript(this.GetType(), "SuccessMessage", script, true);
                            //this.lblMessage.Text = "Duplicate PO Number Not Allowed !!";
                        }
                        using (SqlCommand cmd = new SqlCommand("UPDATE bpms SET amt_rls = @amt_rls,amt_rls_dt=@amt_rls_dt,tds_gst=@tds_gst,tds_it=@tds_it,ld=@ld,sd_pbg=@sd_pbg,instl_chrg=@instl_chrg,othr_ded=@othr_ded,othr_ded_rsn=@othr_ded_rsn,tda=@tda,gt=@gt,Fa_updt_dt=@Fa_updt_dt,updt_b_id=@updt_b_id,updt_b_nm=@updt_b_nm,updt_b_dpt=@updt_b_dpt WHERE Id = @Id"))
                        {
                            cmd.Parameters.AddWithValue("@Id", Label1.Text);
                            cmd.Parameters.AddWithValue("@amt_rls", TextBox1.Text);
                            cmd.Parameters.AddWithValue("@amt_rls_dt", TextBox2.Text);
                            cmd.Parameters.AddWithValue("@tds_gst", TextBox3.Text);
                            cmd.Parameters.AddWithValue("@tds_it", TextBox4.Text);
                            cmd.Parameters.AddWithValue("@ld", TextBox5.Text);
                            cmd.Parameters.AddWithValue("@sd_pbg", TextBox6.Text);
                            cmd.Parameters.AddWithValue("@instl_chrg", TextBox7.Text);
                            cmd.Parameters.AddWithValue("@othr_ded", TextBox8.Text);
                            cmd.Parameters.AddWithValue("@othr_ded_rsn", TextBox9.Text);
                            cmd.Parameters.AddWithValue("@gnrl_rmk", TextBox10.Text);
                            cmd.Parameters.AddWithValue("@tda", TextBox15.Text);
                            cmd.Parameters.AddWithValue("@gt", TextBox16.Text);
                            cmd.Parameters.AddWithValue("@Fa_updt_dt", Label16.Text);
                            cmd.Parameters.AddWithValue("@updt_b_id", Label14.Text);
                            cmd.Parameters.AddWithValue("@updt_b_nm", Label12.Text);
                            cmd.Parameters.AddWithValue("@updt_b_dpt", Label15.Text);
                            cmd.Connection = con;
                            con.Open();
                            cmd.ExecuteNonQuery();
                            con.Close();
                            string message = "Bill  details have been saved successfully.";
                            string script = "window.onload = function(){ alert('";
                            script += message;
                            script += "');";
                            script += "window.location = '";
                            script += Request.Url.AbsoluteUri;
                            script += "'; }";
                            ClientScript.RegisterStartupScript(this.GetType(), "SuccessMessage", script, true);
                        }
                    }
                    // Response.Redirect("fa.aspx");
                }
            }
        }
    }
}
CREATE TABLE [dbo].[bpms] (
    [Id]               INT            IDENTITY (1, 1) NOT NULL,
    [emp_id]           VARCHAR (50)   NULL,
    [emp_nm]           VARCHAR (50)   NULL,
    [dept]             VARCHAR (50)   NULL,
    [p_n]              NCHAR (10)     NULL,
    [agcy]             VARCHAR (50)   NULL,
    [srv_no]           NVARCHAR (50)  NULL,
    [srv_dt]           VARCHAR (50)   NULL,
    [srv_amt]          VARCHAR (50)   NULL,
    [prk_amnt]         VARCHAR (50)   NULL,
    [prk_nm]           VARCHAR (50)   DEFAULT ('NA') NULL,
    [prk_dt]           VARCHAR (50)   DEFAULT ('NA') NULL,
    [mrk_in_fa]        VARCHAR (10)   DEFAULT ('NO') NULL,
    [amt_rls]          VARCHAR (50)   DEFAULT ('NA') NULL,
    [amt_rls_dt]       VARCHAR (50)   DEFAULT ('NA') NULL,
    [tds_gst]          VARCHAR (50)   DEFAULT ('NA') NULL,
    [tds_it]           VARCHAR (50)   DEFAULT ('NA') NULL,
    [ld]               VARCHAR (50)   DEFAULT ('NA') NULL,
    [sd_pbg]           VARCHAR (50)   DEFAULT ('NA') NULL,
    [instl_chrg]       VARCHAR (50)   DEFAULT ('NA') NULL,
    [othr_ded]         VARCHAR (50)   DEFAULT ('NA') NULL,
    [othr_ded_rsn]     VARCHAR (500)  DEFAULT ('NA') NULL,
    [gnrl_rmk]         VARCHAR (500)  DEFAULT ('NA') NULL,
    [stl]              VARCHAR (50)   DEFAULT ('Pending') NULL,
    [tda]              VARCHAR (MAX)  NULL,
    [gt]               VARCHAR (MAX)  NULL,
    [Fa_updt_dt]       VARCHAR (50)   NULL,
    [updt_b_id]        VARCHAR (50)   NULL,
    [updt_b_nm]        VARCHAR (50)   NULL,
    [updt_b_dpt]       VARCHAR (50)   NULL,
    [cnm_inst_dt]      VARCHAR (50)   NULL,
    [phn]              VARCHAR (12)   NULL,
    [eml]              VARCHAR (50)   NULL,
    [inv_no_agnst_srv] VARCHAR (1000) NULL,
    [vchr_no]          VARCHAR (500)  DEFAULT ('NA') NULL,
    [LODGE_DATE]       DATE           DEFAULT (getdate()) NULL,
    PRIMARY KEY CLUSTERED ([Id] ASC)
);