ASHX to download xlsx file

I've got a very strange problem when trying to write an ASHX response. I use it in my web project to allow users to download a generated .xlsx file. First I have a response.redirect from my main page to the .ashx file, and in the .ashx file I generate an excel file and sends it to the response.

This works perfectly when run in Microsoft Visual Studio - My coding envierment, but doesnt work when I export it to the IIS 8.5 server. There all I get is a white page instead of a xlsx file. Ive tried both Response.end and CompleteRequest. If anyone have a clue, please help. (WriteExcelFile works, since it generates a perfect file in coding envierment)

   System.Web.HttpResponse Response = System.Web.HttpContext.Current.Response;

                System.Web.HttpRequest Request = System.Web.HttpContext.Current.Request;

                //Remove block
                System.Data.DataTable myExcelData = new System.Data.DataTable();
                myExcelData.Columns.Add("Tid", typeof(string));
                myExcelData.Columns.Add("Grupp", typeof(string));
                myExcelData.Columns.Add("Felkod", typeof(Int32));
                myExcelData.Columns.Add("FelText", typeof(string));
                myExcelData.Columns.Add("Kommentar", typeof(string));
                myExcelData.Columns.Add("Kommentar2", typeof(string));
                myExcelData.Columns.Add("Severity", typeof(Int32));
                myExcelData.AcceptChanges();
                myExcelData.Rows.Add( "STARTTID",
                   "FELTYP",
                   17,
                   "HEJSAN",
                   "NO COMMENT",
                   "NO COMMENT",
                   23);
                myExcelData.AcceptChanges();
                System.Data.DataSet ds = new System.Data.DataSet();
                ds.Tables.Add(myExcelData);

                //Remove Memorystream block
                System.IO.MemoryStream stream = new System.IO.MemoryStream();
                using (SpreadsheetDocument document = SpreadsheetDocument.Create(stream, SpreadsheetDocumentType.Workbook, true))
                {

                    ExportToExcel.CreateExcelFile.WriteExcelFile(ds, document, "AlarmList");
                }
                stream.Flush();
                stream.Position = 0;

                Response.ClearContent();
                Response.Clear();
                Response.Buffer = true;
                Response.Charset = "";

                //  NOTE: If you get an "HttpCacheability does not exist" error on the following line, make sure you have
                //  manually added System.Web to this project's References.

                Response.Cache.SetCacheability(System.Web.HttpCacheability.NoCache);
                Response.AddHeader("content-disposition", "attachment; filename=" + "header.xlsx");
                Response.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
                byte[] data1 = new byte[stream.Length];
                stream.Read(data1, 0, data1.Length);
                stream.Close();
                Response.BinaryWrite(data1);
                Response.Flush();

                Response.End();

            //    System.Web.HttpContext.Current.Response.SuppressContent = true;  // Gets or sets a value indicating whether to send HTTP content to the client.
            //    System.Web.HttpContext.Current.ApplicationInstance.CompleteRequest(); // Causes ASP.NET to bypass all events 
            //Response kastar alltid exception .end exekveras inte. så vi kör linjen ovan istellet