System.Net.WebException: The underlying connection was closed: The server committed a protocol violation.
 at System.Net.FtpWebRequest.DataStreamClosed(CloseExState closeState)
at System.Net.FtpDataStream.System.Net.ICloseEx.CloseEx(CloseExState closeState)
at System.Net.FtpDataStream.Dispose(Boolean disposing)
at System.IO.Stream.Close()
at System.Net.FtpDataStream.Read(Byte[] buffer, Int32 offset, Int32 size)
at System.IO.StreamReader.ReadBuffer()
at System.IO.StreamReader.ReadLine()

    [TestMethod]
    public async Task GetFilesInParallel()
    {
        var tasks = new List<Task>();
        for(var i = 0; i < 100; i++)
        {
            var task = Task.Run(this.GetFilesAsync);
            tasks.Add(task);
        }

        await Task.WhenAll(tasks).ConfigureAwait(false);
    }

    private async Task<IList<string>> GetFilesAsync()
    {
        var requestUri = "ftp://localhost";
        var request = (FtpWebRequest)WebRequest.Create(requestUri);
        request.Method = WebRequestMethods.Ftp.ListDirectory;
        request.Credentials = new NetworkCredential("anonymous", "foo@bar.com");
        request.KeepAlive = false;

        var files = new List<string>();
        using (var response = await request.GetResponseAsync().ConfigureAwait(false))
        {
            using (var responseStream = response.GetResponseStream())
            {
                using (var reader = new StreamReader(responseStream))
                {
                    string line;
                    while ((line = reader.ReadLine()) != null)
                    {
                        files.Add(Path.GetFileName(line));
                    }

                    reader.Close();
                    responseStream.Close();
                }
            }
        }

        return files;
    }