c# Stream.Seek is giving me a 'NullReferenceException'

I'm losing my mind over this one. Can anyone spot an error in my code following this comment as it is giving me a NullReferenceException error at the point highlighted.... Thanks in advance for any suggestions...

    //retreive the picture from isolated storage
    Stream file = PicturesLoader.LoadFileFromStorage(PhoneApplicationService.Current.State[PictureCrop.PictureStateKey_Url].ToString());
    BitmapImage bi = new BitmapImage();
    bi.SetSource(file);

    //load _pic
    Picture _pic = new Picture();

    _pic.Name = "TempFile";
    _pic.Url = PhoneApplicationService.Current.State[PictureCrop.PictureStateKey_Url].ToString();
    _pic.Height = bi.PixelHeight;
    _pic.Width = bi.PixelWidth;
    _pic.Bitmap = bi;

    //save the new cropped image for later use
    file.Seek(0, SeekOrigin.Begin);
    Ap开发者_开发知识库p._capturedImage.SetSource(file); <------  THROWS ERROR HERE, suggest file  = NullReferenceException ???????????????????

    //Get rid of the stream....
    file.Dispose();

A shot in the dark: probably _capturedImage is the null one.

Either _capturedImage is the null reference, or (supposing App is a field or property rather than a class name) App is returning the null reference.