definition for 'Value' accepting a first argument of type '' could not be found

definition for 'Value' accepting a first argument of type '' could not be
found

Hi I want to display the selected date from my datetimepicker in a
textbox. I have tried the following but get the error on value: DatePicker
does not contain a definition for 'Value' accepting a first argument of
type '' could not be found..
private void datePicker_ValueChanged(object sender, EventArgs e)
{
DateTime date = this.datePicker.Value;
this.txtExpire.Text = date.ToString("dd-mm-yyyy");
}