ClosedXML Excel not working in windows 8

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ASP.NET

MS-Excel

Hi
I have a code which generates Excel file in c# using closedXML.

var workbook = new XLWorkbook();
var worksheet_1 = workbook.Worksheets.Add("Summary Report");
CreateLayout(worksheet_1, dt_Clone, dtS, strHeaderList, strReportHeader, additionalReportHeader);
FillData(ds, worksheet_1, dt_Clone);
worksheet_ProjectionSummary.PageSetup.PageOrientation = XLPageOrientation.Landscape;
string folder_path = Server.MapPath("~\\Reports\\");
string fileName = "SummaryReport_" + Session["Id"].ToString() + ".xlsx";
string fName = folder_path + fileName;

string[] fileEntries = Directory.GetFiles(folder_path);
foreach (string FName in fileEntries)
{
    if (FName.Contains("SummaryReport"))
    {
        System.IO.File.Delete(FName);
    }
}

workbook.SaveAs(fName);

This code works fine with office 2010 and windows 7.
However when I try to generate the same report using windows 8 and office 2013, I get a pop up saying file is corrupted.
When I save the file and re open in windows 8, it is working as expected.
Help me out here. How would i do open the file in windows 8 with out saving it?
Thanks in advance.