C # DSM (Data Source Manager) is not displayed using NTWAIN library

Question

I use the NTWAIN library, found a good solution for interacting with this library, modified it a little. This is actually it:

public class ScanningTwain
    {
        List<Image> ImagesScan;
        DataSource myDS;
        TwainSession session;

        public ScanningTwain()
        {
            ImagesScan = new List<Image>();
        }

        public List<Image> Scan(decimal dpi)
        {
            ImagesScan.Clear();
            
            var appId = TWIdentity.CreateFromAssembly(DataGroups.Image, Assembly.GetExecutingAssembly());
           
            session = new TwainSession(appId);

            session.TransferReady += session_TransferReady;
            session.DataTransferred += session_DataTransferred;
            session.SourceDisabled += session_SourceDisable;

            session.Open();

            IEnumerable<DataSource> lesSources = session.GetSources();
            myDS = lesSources.FirstOrDefault();
            myDS.Open();
        
            PixelType typeCouleur = PixelType.Gray;

            if (myDS.Capabilities.ICapPixelType.CanSet &&
                myDS.Capabilities.ICapPixelType.GetValues().Contains(typeCouleur))
            {
                myDS.Capabilities.ICapPixelType.SetValue(typeCouleur);
            }

            TWFix32 DPI = (float)dpi;

            if (myDS.Capabilities.ICapXResolution.CanSet &&
                myDS.Capabilities.ICapXResolution.GetValues().Contains(DPI))
            {
                myDS.Capabilities.ICapXResolution.SetValue(DPI);
            }

            if (myDS.Capabilities.ICapYResolution.CanSet &&
                myDS.Capabilities.ICapYResolution.GetValues().Contains(DPI))
            {
                myDS.Capabilities.ICapYResolution.SetValue(DPI);
            }

            myDS.Enable(SourceEnableMode.ShowUI, false, System.IntPtr.Zero);

            EventWaitHandle session_SourceDisable_Wait = new EventWaitHandle(false, EventResetMode.AutoReset);
            session_SourceDisable_Wait.WaitOne();
            return ImagesScan;
        }

        void session_DataTransferred(object sender, NTwain.DataTransferredEventArgs e)
        {
            if (e.NativeData != IntPtr.Zero)
            {
                Bitmap img = null;
                //Need to save out the data.
                Stream s = e.GetNativeImageStream();
                BitmapSource bitmapsource = s.ConvertToWpfBitmap();

                using (MemoryStream outStream = new MemoryStream())
                {
                    BitmapEncoder enc = new BmpBitmapEncoder();
                    enc.Frames.Add(BitmapFrame.Create(bitmapsource));
                    enc.Save(outStream);
                    img = new Bitmap(outStream);
                }

                if (img != null)
                {
                    ImagesScan.Add(img);
                }
            }
        }

        void session_SourceDisable(object sender, EventArgs e)
        {
            myDS.Close();
            session.Close();
        }

        void session_TransferReady(object sender, NTwain.TransferReadyEventArgs e)
        {
        }
    }

The error occurs at the line: myDS.Open () ; in the public List <Image> Scan (decimal dpi) method writes that myDS = null , I suppose this is due to the fact that when this line is executed session.Open () ; DSM does not appear so that you can select a scanner. Although I downloaded DSM from the official site. Thank you in advance for your help!