Gzip Comphression Error...

// Will open the file to be compressed
                FileStream fsSource;

                // Will write the new zip file
                FileStream fsDest;
                GZipStream gzCompressed;

                using (fsSource = new FileStream(aFile.FullName, FileMode.Open, FileAccess.Read, FileShare.Read))
                {
                    // Open the FileStream to write to
                    string archivedFileName = Path.GetFileNameWithoutExtension(aFile.FullName);
                    archivedFileName = Path.Combine(archiveDirectory.FullName, archivedFileName + ".gz");
                    using (fsDest = new FileStream(archivedFileName, FileMode.OpenOrCreate, FileAccess.Write))
                    {
                        // Will hold the compressed stream created from the destination stream
                        using (gzCompressed = new GZipStream(fsDest, CompressionMode.Compress, true))
                        {
                            byte[] buffer = new byte[4096];
                            int numRead;
                            while ((numRead = fsSource.Read(buffer, 0, buffer.Length)) != 0)
                            {
                                gzCompressed.Write(buffer, 0, numRead);
                            }

                            // Close the streams
                            fsSource.Close();
                            gzCompressed.Close();
                            fsDest.Close();
                        }
                    }
                }

FileInfo fi = "your file";
// Get the stream of the source file.
            using (FileStream inFile = fi.OpenRead())
            {
                // Get original file extension, for example "doc" from report.doc.gz.
                string curFile = fi.FullName;
                string origName = curFile.Remove(curFile.Length - fi.Extension.Length) +".txt";

                //Create the decompressed file.
                using (FileStream outFile = File.Create(origName))
                {
                    using (GZipStream Decompress = new GZipStream(inFile,
                            CompressionMode.Decompress))
                    {
                        //Copy the decompression stream into the output file.
                        byte[] buffer = new byte[4096];
                        int numRead;
                        while ((numRead = Decompress.Read(buffer, 0, buffer.Length)) != 0)
                        {
                            outFile.Write(buffer, 0, numRead);
                        }
                    }
                }
            }