public DateTime EvaluateDateTime(Report rpt, Row row)
 {
     try
     {
         return(_Expr.EvaluateDateTime(rpt, row));
     }
     catch (Exception e)
     {
         string err = String.Format("Exception evaluating {0}.  {1}", _Source, e.Message);
         ReportError(rpt, 4, err);
         return(DateTime.MinValue);
     }
 }