Crc32 is broken

Hi

Task:

I want to create zip archives on the fly containing a certain number of Excel files.  Excel files are created from the database also on the fly.

Problem:

I get an error when trying to unzip the resulting archive "Archive is damaged or has the wrong format". In archive i see that Crc32 is 00000000 for evry files. Also a have no errors when only one file is archiv.

Code:

//load excel files to archive

using (var stream = new MemoryStream())

            {

                using (var zipPackage = new ZipHelper(stream))

                {

                    foreach (var dt in res)

                    {

                        MemoryStream ms = new MemoryStream();

                        XLWorkbook wb = new XLWorkbook();

                         wb.Worksheets.Add(dt);

                         wb.SaveAs(ms);

                            zipPackage.Add(ms,

                                string.Format(CultureInfo.InvariantCulture, "{0}.xlsx",

                                    string.Format(CultureInfo.InvariantCulture, dt.TableName)));

                        ms.Flush();

                        ms.Close();

                    }

                }

                stream.Flush();

                LoadZipToResponse(stream);

            }

//Add mehod

public ZipHelper Add(MemoryStream ms, string cleanName)

        {

            var zipEntry = new ZipEntry(cleanName)

            {

                DateTime = DateTime.Now,

                Size = ms.Length

            };

            zipEntry.CompressionMethod = CompressionMethod.Stored;

            _crc.Reset();

            _crc.Update(ms.ToArray());

            zipEntry.Crc = _crc.Value;

            _zipStream.PutNextEntry(zipEntry);

            _zipStream.Write(ms.GetBuffer(), 0, (int)ms.Length);

            _zipStream.CloseEntry();

            return this;

        }

//LoadZipToResponse 

        private void LoadZipToResponse(MemoryStream stream)

        {

            Response.ContentType = "application/zip";

            Response.AppendHeader("content-disposition", "attachment; filename=\"" + "DataExport.zip" + "\"");

            Response.CacheControl = "Private";

            Response.Cache.SetExpires(DateTime.Now.AddMinutes(5));

            Page.Response.BinaryWrite(stream.GetBuffer());

            stream.Close();

            Response.Flush();

            Response.End();

        }