Why do the asp.net gods hate me?

Why is my html table not recognized?

I am trying to dynamically add rows to my html table like this:

    private void AddTableRow( DateTime d8DayOff )
    {
      HtmlTableRow tRow = new HtmlTableRow();
      HtmlTableCell cellDate = new HtmlTableCell();
      HtmlTableCell cellOccasion = new HtmlTableCell();
      Label lblDate = new Label();
      Label lblOccasion = new Label();
      lblDate.Text = d8DayOff.ToShortDateString();
      lblOccasion.Text = GetDayOffReason(d8DayOff);
      cellDate.Controls.Add(lblDate);
      cellOccasion.Controls.Add(lblOccasion);
      tRow.Cells.Add(cellDate);
      ...