Unzipping a .gz file

Question

I'm a student I'm trying to unzip a gz file but it gives following error message:

Stating the magic number in GZip header is not correct, here is the code, I'really thannk full if any1 could let me know what mistake I'm doing

        FileInfo fileToDecompress = new FileInfo(dirpath);
        {
            Decompress(fileToDecompress);
        }

        Dts.TaskResult = (int)ScriptResults.Success;
    }

    public static void Decompress(FileInfo fileToDecompress)
    {
        using (FileStream originalFileStream = fileToDecompress.OpenRead())
        {
            string currentFileName = fileToDecompress.FullName;
            string newFileName = currentFileName.Remove(currentFileName.Length - fileToDecompress.Extension.Length);

            using (FileStream decompressedFileStream = File.Create(newFileName))
            {
                using (GZipStream decompressionStream = new GZipStream(originalFileStream, CompressionMode.Decompress,true))
                {
                    decompressionStream.CopyTo(decompressedFileStream);
                    Console.WriteLine("Decompressed: {0}", fileToDecompress.Name);
                }
            }
        }
    }

    #region ScriptResults declaration
    /// <summary>
    /// This enum provides a convenient shorthand within the scope of this class for setting the
    /// result of the script.
    /// 
    /// This code was generated automatically.
    /// </summary>
    enum ScriptResults
    {
        Success = Microsoft.SqlServer.Dts.Runtime.DTSExecResult.Success,
        Failure = Microsoft.SqlServer.Dts.Runtime.DTSExecResult.Failure
    };
    #endregion

}

Answer 1

That means what it says. What you think is a gzip file is not, and does not start with 0x1f 0x8b.