Not bad! Your grasp of the basics is good, but you perhaps need to work a little on the details which make a scene like that believable. Look at your smaller planets for example - they do not have the shadows in the right place in relation to the sun... and they are also seem to 'pop out' of the background, whereas moons would usually be smaller and, therefore, darker than big planets in the foreground.
Oh, and what error did you get BTW? I'm keen to make sure everything works as desired...
