void flyGrid1_ColumnFilterValidate(object sender, Column column, System.Collections.ArrayList filterList)
{
    CultureInfo ivCulture = CultureInfo.InvariantCulture;

    if (column.FieldName == \"col1\")
    {
        filterList.Clear();
        filterList.Add(new FilterHelper(\"[All]\", FilterMode.All));
        filterList.Add(new FilterHelper(\"[Custom]\", FilterMode.Custom));

        List dates = new List();
        foreach(Node node in flyGrid1.Rows.Items)
        {
            DateTime date = ((DateTime)node.GetCellValue(0)).Date;
            if (!dates.Contains(date))
            {
                dates.Add(date);

                filterList.Add(new FilterHelper(date.ToShortDateString(),
                    new FilterItem[]
                    {
                    new FilterItem(date           , FilterOperator.And, ConditionOperator.GreaterThanOrEqual),
                    new FilterItem(date.AddDays(1), FilterOperator.And, ConditionOperator.LessThan)
                    }));

            }
        }
    }
}

. . .

this.dateTimeColumn1.AllowFiltering = true;
this.dateTimeColumn1.Caption = \"Date\";
this.dateTimeColumn1.FieldName = \"col1\";
this.dateTimeColumn1.ImageKey = null;
this.dateTimeColumn1.MaxValue = new System.DateTime(9999, 12, 31, 23, 59, 59, 999);
this.dateTimeColumn1.MinValue = new System.DateTime(((long)(0)));
this.dateTimeColumn1.State = NineRays.Windows.Forms.Grids.ColumnState.DropDownBtnUp;
this.dateTimeColumn1.Width = 120;

DataTable data = new DataTable();
data.Columns.Add(\"col1\", typeof(DateTime));
data.Rows.Add(new DateTime(2007, 12, 12));
data.Rows.Add(new DateTime(2005, 12, 12));
data.Rows.Add(new DateTime(1995, 12, 12));

flyGrid1.Rows.DataSource = data;

filterList.Clear();
filterList.Add(new FilterHelper(\"[All]\", FilterMode.All));
filterList.Add(new FilterHelper(\"[Custom]\", FilterMode.Custom));

List dates = new List();


foreach (NodeBase node in flyGrid1.Rows.Items)
{
    object cellValue = node.GetCellValue(0);
    if (cellValue != null)
    {
        DateTime date = ((DateTime)cellValue).Date;
        if (!dates.Contains(date))
        {
            dates.Add(date);

            filterList.Add(new FilterHelper(date.ToShortDateString(),
                new FilterItem[]
                {
                new FilterItem(date           , FilterOperator.And, ConditionOperator.GreaterThanOrEqual),
                new FilterItem(date.AddDays(1), FilterOperator.And, ConditionOperator.LessThan)
                }));

        }
    }
}

I got your demo code for this and watered it down and found that your demo works only if you bind to DataTable, if you bind to List or if you run data in unbound mode (like get data from DataTable OrderDetails and put it into a row - grid.Rows.Items.Add(new Node(new object []....) then it stops to work....