save the datagridview record using check box in csharp

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C#

Design as follows;

Faculty Code Combo box

Month calendar (calendar Control)

in Datagridview as follows;

Seleck(checkbox) Dates


when i select the any month in the month calendar that month all dates is dispaly into the datagridivew.

using check box i select any of the date in the datagridview and save in the database.

For that my code as follows;

private void Btn_Save_Click(object sender, EventArgs e)
 {

            int i = 0;
            if(Convert.ToString(DGVCalendar[1,i].Value) == "True")
                 {
                    sql = "insert into Tb_Faculty_Availability ([Faculty_code],[Available_date],)";
                    sql = sql + " values('" + cb_Faculty_Code.Text + "','" + Convert.ToDateTime(DGVCalendar.Rows[i].Cells[2].Value.ToString()) + "')";
                    
                    try
                    {
                        GFun.Error = "";
                        GFun.InsertAccessData(sql);
                        if (GFun.Error.ToString() != "")
                        {
                            MessageBox.Show(GFun.Error.ToString(), "Error");
                            this.Cursor = Cursors.Arrow;
                            return;
                        }
                        GFun.OleDbCon.Close();
                        MessageBox.Show("Records Inserted Successfully", "Record Inserted", MessageBoxButtons.OK, MessageBoxIcon.Information);
                    }

                    catch (Exception Ex)
                    {
                        MessageBox.Show(Ex.ToString(), "Error");
                        this.Cursor = Cursors.Arrow;
                        return;
                    }

         }
}

when i click the save button the record is not saving in the database.

From my above code what is the problem.

Please help me.

Regards,
Narasiman P.