In Autocad Civil 3d 2011 I have a fairly low resolution image that is x-refed into the base file on layer X-ref images. Neither the layer nor the image show up when the file is openned with Impression 3. I am below the pixel resolution limits with image size.
I have sort of resolved the problem by cropping the X-ref image down to a size that falls within the view of the viewport.
It took a bit of guesswork to get it the right size, but it does work.
This may be something for Autodesk to look at. I import air photo's into my background and work on top of them with various proposals. Playing around with cropping et al, is time consuming.