asp.net 压缩文件夹问题

我做的是压缩后下载，但是在压缩稍微大一点的文件时候第二次压缩就报错说压缩文件被进程占用，小文件可以大压缩文件估计20M
源码：    public static void Compress(string dirPath, string fileName)
        {
            ArrayList list = new ArrayList();
            foreach (string f in Directory.GetFiles(dirPath))
            {
                byte[] destBuffer = File.ReadAllBytes(f);
                SerializeFileInfo sfi = new SerializeFileInfo(f, destBuffer);
                list.Add(sfi);
            }
            IFormatter formatter = new BinaryFormatter();
            using (Stream s = new MemoryStream())
            {
                formatter.Serialize(s, list);
                s.Position = 0;
                CreateCompressFile(s, fileName);

                s.Close();
                s.Dispose();
            }

        }
          private static void CreateCompressFile(Stream source, string destinationName)
        {
            using (Stream destination = new FileStream(destinationName, FileMode.Create, FileAccess.Write))
            {
                using (GZipStream output = new GZipStream(destination, CompressionMode.Compress))
                {
                    byte[] bytes = new byte[1024];
                    int n;
                    while ((n = source.Read(bytes, 0, bytes.Length)) != 0)
                    {
                        output.Write(bytes, 0, n);
                    }
                    //output.Dispose();
                    //output.Close();


                }

                //destination.Close();
                //destination.Dispose();

            }
        }

        [Serializable]
        class SerializeFileInfo
        {
            public SerializeFileInfo(string name, byte[] buffer)
            {
                fileName = name;
                fileBuffer = buffer;
            }

            string fileName;
            public string FileName
            {
                get
                {
                    return fileName;
                }
            }

            byte[] fileBuffer;
            public byte[] FileBuffer
            {
                get
                {
                    return fileBuffer;
                }
            }
        }
     --------------------编程问答-------------------- 没有目测出问题来，下载的时候有关闭文件读取？ --------------------编程问答-------------------- 是不是重复压缩，或没释放文件

补充：.NET技术 ,  C#