[C#] Compression Gzip, fonctionne plus

"C:\........ fichier.exe"
Le paramètre est incorrect.

byte[] OBuffer = new byte[OFileStream.Length];
                    // Read whole FileStream
                    OFileStream.Read(OBuffer, 0, System.Convert.ToInt32(OFileStream.Length));
                    // Close FileStream
                    OFileStream.Close();
                    // Create the file new file
                    OFileStream = new FileStream(fileTextbox.Text, FileMode.Create);

                    // Compress data
                    GZipStream OGZipStream = new GZipStream(OFileStream, CompressionMode.Compress, false);
                    // Write the compressed data in the file
                    OGZipStream.Write(OBuffer, 0, OBuffer.Length);
                    // Close GZipStream
                    OGZipStream.Close();

using System;
using System.IO;
using System.IO.Compression;

namespace zip
{

    public class Program
    {

        public static void Main()
        {
            // Path to directory of files to compress and decompress.
            string dirpath = @"c:\users\public\reports";

            DirectoryInfo di = new DirectoryInfo(dirpath);

            // Compress the directory's files.
            foreach (FileInfo fi in di.GetFiles())
            {
                Compress(fi);

            }

            // Decompress all *.gz files in the directory.
            foreach (FileInfo fi in di.GetFiles("*.gz"))
            {
                Decompress(fi);

            }


        }

        public static void Compress(FileInfo fi)
        {
            // Get the stream of the source file.
            using (FileStream inFile = fi.OpenRead())
            {
                // Prevent compressing hidden and 
                // already compressed files.
                if ((File.GetAttributes(fi.FullName) 
                	& FileAttributes.Hidden)
                	!= FileAttributes.Hidden & fi.Extension != ".gz")
                {
                    // Create the compressed file.
                    using (FileStream outFile = 
                    			File.Create(fi.FullName + ".gz"))
                    {
                        using (GZipStream Compress = 
                        	new GZipStream(outFile, 
                        	CompressionMode.Compress))
                        {
                            // Copy the source file into 
                            // the compression stream.
                        inFile.CopyTo(Compress);

                            Console.WriteLine("Compressed {0} from {1} to {2} bytes.",
                                fi.Name, fi.Length.ToString(), outFile.Length.ToString());
                        }
                    }
                }
            }
        }

        public static void Decompress(FileInfo fi)
        {
            // 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);

                //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.
            		    Decompress.CopyTo(outFile);
            		    
                        Console.WriteLine("Decompressed: {0}", fi.Name);

                    }
                }
            }
        }

    }
}