位图保存为流，报Abstract error,该如何处理

位图保存为流，报Abstract error
procedure   TForm1.btnSaveAsClick(Sender:   TObject);
var
    aJpg:   TJpegImage;
    tsStream:   TStream;
begin
    aJpg   :=   TJpegImage.Create;
    tsStream   :=   TStream.Create;
    try
        Image1.Picture.Bitmap.SaveToStream(tsStream);
        aJpg.LoadFromStream(tsStream);
        aJpg.SaveToFile( 'cc.jpg ');
    finally
        aJpg.Free;
        tsStream.Free;
    end;
end;


在“Image1.Picture.Bitmap.SaveToStream(tsStream);”时报错：Abstract   error

[解决办法]
在 aJpg.LoadFromStream(mmStream); 之前加一名句:mmStream.Position := 0;