OpenXml creates corrupted excel when there are large amount of row

I'm implemented this method to create an excel spreadsheet using openxml. It works 100% of the time when the number of rows are under around 15000 rows otherwise the excel will sometimes come out corrupted with excel giving me the message "The workbook cannot be opened or repaired by Microsoft Excel because it is corrupt". Any explanations please?

    public static SaveResults CreateExcelDocument(Stream excelStream, List<ExportColumns> columns, IEnumerable data, string sheetName)
    {
        SaveResults results = new SaveResults();
        results.Status = SAVE_STATUS.ERROR;

        try
        {
            if ((sheetName == null) || (sheetName.Trim() == ""))
                sheetName = "Report";
        }
        catch { }

        try
        {
            using (SpreadsheetDocument document = SpreadsheetDocument.Create(excelStream, SpreadsheetDocumentType.Workbook))
            {

                // Add a WorkbookPart to the document.
                WorkbookPart workbookPart = document.AddWorkbookPart();
                workbookPart.Workbook = new Workbook();

                // Add a WorksheetPart to the WorkbookPart.
                WorksheetPart worksheetPart = workbookPart.AddNewPart<WorksheetPart>();
                SheetData sheetData = new SheetData();
                worksheetPart.Worksheet = new Worksheet(sheetData);

                // Add Sheets to the Workbook.
                Sheets sheets = document.WorkbookPart.Workbook.AppendChild<Sheets>(new Sheets());

                Sheet sheet = new Sheet()
                {
                    Id = workbookPart.GetIdOfPart(worksheetPart),
                    SheetId = 1,
                    Name = sheetName
                };

                //get the type of the object in the list
                Type myListElementType = data.GetType().GetGenericArguments().Single();

                // Constructing header
                Row row = new Row();

                foreach (ExportColumns exportColumn in columns)
                {
                    if (!string.IsNullOrEmpty(exportColumn.display.Trim()))
                    {
                        row.Append(ConstructCell(exportColumn.display, CellValues.String));
                    }
                }

                // Insert the header row to the Sheet Data
                sheetData.AppendChild(row);


                foreach (var obj in data)
                {
                    row = new Row();

                    foreach (ExportColumns exportColumn in columns)
                    {
                        if (!string.IsNullOrEmpty(exportColumn.display.Trim()))
                        {
                            object cellObject = null;

                            try
                            {
                                if (myListElementType.GetProperty(exportColumn.name) == null)
                                {
                                    cellObject = ((IDictionary<string, object>)obj)[exportColumn.name];
                                }
                                else
                                {
                                    cellObject = myListElementType.GetProperty(exportColumn.name).GetValue(obj);
                                }

                                //if the value is null bad things happen so put in a cell with a null value string
                                if (cellObject == null)
                                {
                                    // create cell with data
                                    row.Append(
                                    ConstructCell(null, CellValues.String)
                                    );
                                    continue;
                                }

                                if (cellObject is DateTime)
                                {
                                    // create cell with data
                                    DateTime dtValue = (DateTime)cellObject;
                                    row.Append(
                                    ConstructCell(dtValue.ToOADate().ToString(), CellValues.String)
                                    );
                                }
                                else if (IsNumber(cellObject))
                                {
                                    // create cell with data
                                    row.Append(ConstructCell(cellObject.ToString(), CellValues.Number));
                                }
                                else
                                {
                                    // create cell with data
                                    row.Append(ConstructCell(SanitizeXmlString(cellObject.ToString()), CellValues.String));
                                }
                            }
                            catch (Exception ex2)
                            {
                                row.Append(ConstructCell(SanitizeXmlString(exportColumn.path.Trim()), CellValues.String));

                            }
                        }
                    }
                    sheetData.AppendChild(row);
                }

                sheets.Append(sheet);

                worksheetPart.Worksheet.Save();
                document.Close();
            }

            results.Status = SAVE_STATUS.OK;
        }
        catch (Exception ex)
        {
            Logger.Exception.Error("Export Error", ex);

            results.Exception = new ExceptionData(ex);
            results.Status = SAVE_STATUS.ERROR;
        }

        return results;
    }

    private static Cell ConstructCell(string value, CellValues dataType)
    {
        return new Cell()
        {
            CellValue = new CellValue(value),
            DataType = new EnumValue<CellValues>(dataType)
        };
    }