Listbox items Check - unchecked

/// Listbox items unchecked from another event
if (lstBoxOrderNo1.CheckedItems.Count > 0)
    {
        int count = lstBoxOrderNo1.CheckedItems.Count;
        for (int i = 0; i < count; i++)
        {
            lstBoxOrderNo1.SetItemChecked(lstBoxOrderNo1.CheckedIndices[0], false);
        }                       
    }


/// Listbox items unchecked on event fire
private void lstBoxOrderNo1_ItemCheck(object sender, ItemCheckEventArgs e)
{
    e.NewValue = CheckState.Unchecked;
}

SelectAll CheckBox

        CheckBox HeaderCheckBox = null;
        private void Load_Grid_Data(string CodeStr)
        {
            try
            {
                grdData = iManipulator.GetDataSet("[dbo].[proll_populate_attendance_early_out_approval_grid_sp_1] '" +CodeStr.ToString().Trim()+"','" + compCode + "','" + deptCode + "','" + sectionCode + "','" + unitCode + "','" + lineCode + "','" + desig + "','" + empList + "','" + date + "'").Tables[0].Copy();

                grdGroupLeave.DataSource = grdData;
                initGroupLeaveGrid();
  
                //Adding Header checkBox for select All
                HeaderCheckBox = new CheckBox();
                
               //Place the Header CheckBox in the Location of the Header Cell.
                Point headerCellLocation = this.grdGroupLeave.GetCellDisplayRectangle(0, -1, true).Location;
                HeaderCheckBox.Location = new Point(headerCellLocation.X + 8, headerCellLocation.Y + 2);
                HeaderCheckBox.BackColor = Color.White;

               ////Assign Click event to the Header CheckBox.
                //headerCheckBox.Click += new EventHandler(HeaderCheckBox_Clicked);
                
                //Assign CheckedChanged event to the Header CheckBox.
                HeaderCheckBox.CheckedChanged += new EventHandler(HeaderCheckBox_CheckedChanged);
 
                HeaderCheckBox.Size = new Size(15, 15);
                this.grdGroupLeave.Controls.Add(HeaderCheckBox);
            }
            catch (Exception errExp)
            {
                MessageBox.Show(errExp.Message,Application.ProductName,MessageBoxButtons.OK,MessageBoxIcon.Error);
            }
        }
        
        private void initGroupLeaveGrid()
        {
            iDBGrid.gridInit(grdGroupLeave);

            grdGroupLeave.Columns[0].HeaderText = ""; /// Must Empty CheckBox Header Name

            grdGroupLeave.Columns[0].Width = 30;
            grdGroupLeave.Columns[9].Visible = false;
            grdGroupLeave.Columns["LcScBuyer"].Visible = false;  ///with column name
            grdGroupLeave.Columns[1].ReadOnly = true;
            grdGroupLeave.Columns[2].Frozen = true;
            grdLcScMapping.Columns["LcNo"].DefaultCellStyle.BackColor = Color.Wheat;

            grdGroupLeave.Refresh();
            grdGroupLeave.AllowUserToDeleteRows = false;
        }

        
        //Defination of CheckedChanged event of Header CheckBox. 
         private void HeaderCheckBox_CheckedChanged(object sender, EventArgs e)
        {
            try
            {
                if (HeaderCheckBox.Checked)
                {
                    for (int i = 0; i < grdGroupLeave.Rows.Count; i++)
                    {                        
                        grdGroupLeave[0, i].Value = true; /// Check all
                    }
                }
                else
                {
                    for (int i = 0; i < grdGroupLeave.Rows.Count; i++)
                    {
                        grdGroupLeave[0, i].Value = false;    /// UnCheck all               
                    }                    
                }
            }
            catch (Exception)
            {
                throw;
            }
        }
        
        private void ClearGrid()
        {
            DataTable empdt = new DataTable();
            grdData = empdt.Copy();
            Load_Grid_Data();           
            grdGroupLeave.Controls.Clear(); /// clear Header Checkbox
            grdGroupLeave.Refresh();
        }