请教Epplus复制Sheet，当存在CheckBox时报错

[ufo20020427]

       using (ExcelPackage excel = new ExcelPackage(new FileInfo("d:\\1.xlsx")))
            {
                excel.Workbook.Worksheets.Copy("Sheet1", "Sheet2");

                excel.SaveAs(new FileInfo("d:\\2.xlsx"));  //  InnerException = {"Cannot access a closed Stream."}
            }

上面代码，会把1.xlsx的Sheet1复制到Sheet2，是正常的。
但当Sheet1中存在CheckBox（Form Control)时，则会异常报错。“Cannot access a closed Stream”

请问该如何处理。谢谢！