check the record present in another table using data reader in Csharp .net

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C#

Data Base Design as follows in Ms Access ;

Table Name (Tb_Delcared_Holidays)
HolidayDate Datetime
Reason Text

In Database Records as follows;

HolidayDate Reason
2/22/2013 Holiday
2/25/2013 Holiday

Design as follows;

Faculty Code combobox
Calendar (month Calendar)

Datagrdiview


In combobox all faculty code retrieved from the table and display in to the Combobox.

when i select the calendar that month all date is display in to the datagridview .

when i select the Feburary month in calendar that month all date display in datagridview.

I want to check one condition,when display the date in datagrdiview,

For february month the below two dates is holiday in the Leave Table.
2/22/2013 Leave
2/25/2013 Leave

When i display the date in datagridview,for the above dates in datagridview, the user did not able to select the two dates


Code as follows;

private void Faculty_Available_Calendar_DateChanged(object sender, DateRangeEventArgs e)
{
    //selected month all dates  display in datagridiview
    DGVCalendar.Rows.Clear();
    DateTime dt1 = Faculty_Available_Calendar.SelectionStart;
    dt1 = new DateTime(dt1.Year, dt1.Month, 1);
    DateTime dt2 = dt1.AddMonths(1);
    int numDays = (dt2 - dt1).Days;

    if (DGVCalendar.RowCount < numDays)
    {
        DGVCalendar.RowCount = numDays;
    }

    int row = 0;
    while (dt1 < dt2)
    {
        DGVCalendar.Rows[row].Cells[1].Value = dt1.ToString("dd-MMM-yyyy");
        DGVCalendar.Rows[row].Cells[0].Value = true;  //All checkbox Checked Defaulty 
        if (dt1.DayOfWeek == DayOfWeek.Sunday)
        {
            DGVCalendar.Rows[row].ReadOnly = true;
            DGVCalendar.Rows[row].Cells[0].Value = false;
            DGVCalendar.Rows[row].Cells[0].Style.BackColor = Color.Orange;
            DGVCalendar.Rows[row].Cells[1].Style.BackColor = Color.Orange;
            DGVCalendar.Rows[row].Cells[2].Style.BackColor = Color.Yellow;
            DGVCalendar.Rows[row].Cells[2].Style.ForeColor = Color.Red;
            DGVCalendar.Rows[row].Cells[2].Value = "Sunday";
        }

        sql = "select format(HolidayDate   ,'mm dd yyyy') as Holdate, [Reason] from Tb_Delcared_Holidays where Holidaydate = '" + DGVCalendar.Rows[row].Cells[1].ToString() + "'";
        dr = GFun.ReadAcessSql(sql);
        dr.Read();
        if (dr.HasRows == true)
        {
            DGVCalendar.Rows[row].Cells[1].Style.BackColor = Color.Blue;
            DGVCalendar.Rows[row].Cells[2].Value = dr[0].ToString();
        }

        dt1 = dt1.AddDays(1);
        row++;
    }
}

the above code, in the datagridview for the selected month date, display in datagridview,if the
any of the date is holiday in Tb_Declared_Holidays table,

that date should be shown in different color,user should not select the date.

from my above when i run error shows as follows.
Invalid attempt to call read when reader is closed.

the above shows in the below line as follows;

sql = "select format(HolidayDate   ,'mm dd yyyy') as Holdate, [Reason] from Tb_Delcared_Holidays where Holidaydate = '" + DGVCalendar.Rows[row].Cells[1].ToString() + "'";
dr = GFun.ReadAcessSql(sql);
dr.Read(); [Invalid attempt to call  read when reader is closed]
if (dr.HasRows == true)
{
    DGVCalendar.Rows[row].Cells[1].Style.BackColor = Color.Blue;
    DGVCalendar.Rows[row].Cells[2].Value = dr[0].ToString();
}

dr.read(); line error shows Invalid attempt to call read when reader is closed.

what is the problem in my above code please help me.