using OfficeOpenXml;
using System.IO;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var package = new ExcelPackage())
            {
                var book = package.Workbook;
                var dataSheet = package.Workbook.Worksheets.Add("Data");
                var pivotSheet = package.Workbook.Worksheets.Add("Pivot");
                dataSheet.Cells[1, 1].Value = "<";  //タイトル行が"<"を含むと例外 (ただし">"ならばOK)
                dataSheet.Cells[2, 1].Value = "<";  //データ行ならOK
                pivotSheet.PivotTables.Add(pivotSheet.Cells[1, 1], dataSheet.Cells[1, 1, 2, 1], "Table"); //ここで例外が発生する
                package.SaveAs(new FileInfo("test.xlsx"));
            }
        }
    }
}