扫描图像文件时检测到断开连接的上下文

>我正在尝试在我的WPF应用程序，Caliburn Micro和Windows.Device.Scanners中使用进纸扫描仪扫描文件。该应用程序在第一次尝试扫描时工作正常，但是当我关闭视图并重新打开它时，Visual Studio 在扫描后给我错误"检测到断开连接的上下文"。

if (!IsScanning)
{
    ImageScannerScanResult result=null;
    IsScanning = true;
    result= await myScanner.ScanFilesToFolderAsync(ImageScannerScanSource.Feeder, folder).AsTask(cancellationToken.Token, progress);
    if (result.ScannedFiles.Count > 0)
    {
        try
        {
            StorageFile file = result.ScannedFiles[0];
            System.Drawing.Bitmap Bit = new System.Drawing.Bitmap(file.Path);
            Execute.OnUIThread(() =>
            {
                _Image = Utils.BitmapToBitmapSource(Bit);
                NotifyOfPropertyChange(() => Image);
            });
            IsScanning = false;
        }
        catch(Exception e)
        {
            IsScanning = false;
        }

这是OnDeactivate((

protected override void OnDeactivate(bool close)
{
    base.OnDeactivate(close);
    _CurrentScannerDeviceId = null;
    if (scannerWatcher != null)
    {
        scannerWatcher.Added -= OnScannerAdded;
        scannerWatcher.Removed -= OnScannerRemoved;
        scannerWatcher.EnumerationCompleted -= OnScannerEnumerationComplete;
        if (scannerWatcher.Status == DeviceWatcherStatus.Started)
        {
            scannerWatcher.Stop();
        }
        scannerWatcher = null;
    }
    if(cancellationToken!=null)
        cancellationToken.Cancel();
    GC.Collect();
}