Transparent background after rotate image

rotate.BackgroundColor = Aurigma.GraphicsMill.RgbColor.Transparent;

private void AvandceCombine()
		{
			
			//Load background image
			Aurigma.GraphicsMill.Bitmap bitmap = 
				new Aurigma.GraphicsMill.Bitmap(@"D:\Program Files\Aurigma\Graphics Mill 3.5 for .NET 1.1\Web Demos Source Code\GraphicsMillWebCS\cooler.png".Replace(@"\","/"));


			//Load small image (foreground image)
			Aurigma.GraphicsMill.Bitmap smallBitmap = 
				new Aurigma.GraphicsMill.Bitmap(@"D:\Program Files\Aurigma\Graphics Mill 3.5 for .NET 1.1\Web Demos Source Code\GraphicsMillWebCS\500off.png".Replace(@"\","/"));

			PixelFormatConverter pixelFormatConverter = new PixelFormatConverter();
			pixelFormatConverter.DestinationPixelFormat = PixelFormat.Format24bppRgb;
			pixelFormatConverter.ApplyTransform(smallBitmap);

			//Rotate at 5 degrees with medium quality
			Aurigma.GraphicsMill.Transforms.Rotate rotate =
				new Aurigma.GraphicsMill.Transforms.Rotate();
			rotate.Angle = 30;
			[b]rotate.BackgroundColor = Aurigma.GraphicsMill.RgbColor.Transparent;[/b]
			rotate.InterpolationMode = Aurigma.GraphicsMill.Transforms.InterpolationMode.MediumQuality;
						
			if (rotate.IsPixelFormatSupported(PixelFormat.Format24bppRgb))
				[b]rotate.ApplyTransform(smallBitmap);[/b]

			//Draw foreground image on background with transparency
			smallBitmap.Draw(bitmap, 10, 110, 
				smallBitmap.Width, smallBitmap.Height, 
				Aurigma.GraphicsMill.Transforms.CombineMode.Alpha, 1f, 
				Aurigma.GraphicsMill.Transforms.InterpolationMode.LowQuality);

			bitmap.Save(@"C:/background.png");
			


		}