New Post: Error saving to memory stream

Hello,

I'm saving the workbook to a MemoryStream and I'm getting the following error:
"An item with the same key has already been added."

Here's the stack trace:
at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource)
at System.Collections.Generic.Dictionary2.Insert(TKey key, TValue value, Boolean add)
at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable1 source, Func2 keySelector, Func2 elementSelector, IEqualityComparer1 comparer)
at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable1 source, Func2 keySelector, Func2 elementSelector)
at ClosedXML.Excel.XLWorkbook.GenerateWorksheetPartContent(WorksheetPart worksheetPart, XLWorksheet xlWorksheet, SaveContext context)
at ClosedXML.Excel.XLWorkbook.CreateParts(SpreadsheetDocument document)
at ClosedXML.Excel.XLWorkbook.CreatePackage(Stream stream, Boolean newStream)
at ClosedXML.Excel.XLWorkbook.SaveAs(Stream stream)

__Here's my code:

public static void WriteFileToClient(HttpResponse response, XLWorkbook workbook)
        {
            response.Clear();
            response.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
            response.AddHeader("content-disposition", "attachment;filename=\"Report.xlsx\"");
            using (var memoryStream = new MemoryStream())
            {
                workbook.SaveAs(memoryStream);
                memoryStream.WriteTo(response.OutputStream);
                memoryStream.Close();
            }
            response.End();
        }

Can you help?

Thanks. :)