excel 写入并打开问题

Question

   Excel.Application xapp = new Excel.Application();
                    string excelfilepath = Server.MapPath("~/SysManager/template.xls");
                    Excel.Workbook xbook = xapp.Workbooks._Open(excelfilepath, Missing.Value, Missing.Value,
                                            Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value,
                                            Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value);                    Excel.Worksheet xsheet = (Excel.Worksheet)xbook.Sheets[1];                    Excel.Range rng2 = xsheet.get_Range("A4", Missing.Value);
                    rng2.Value2 = "10";                    Excel.Range rng3 = xsheet.get_Range("B4", Missing.Value);
                    rng3.Value2 = "20";                    xbook.SaveAs(Server.MapPath("~/SysManager/template.xls"), Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value,
                        Excel.XlSaveAsAccessMode.xlNoChange, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value);
                    Excel.Application excel = new Excel.Application(); //引用Excel对象 
                    Excel.Workbook book = excel.Application.Workbooks.Add(Server.MapPath("~/SysManager/template.xls"));
                    //引用Excel工作簿  
                    excel.Visible = true; //使Excel可视  为什么saveas会报excel只读文件呢？