For flatbed scanner images, please make sure you've changed the Camera Motion setting (on the Import page) to Planar Motion.
When you switch to the Stitch page, ICE aligns as many images as it can, then composites them together into a single image. At the bottom of the window, ICE reports how many images it was able to align. Did it align all 4 images in your
case? If not, perhaps there isn't enough overlap between the scans, or there aren't enough significant features in the overlapping areas for ICE to find good matches.
Hope this helps. If not, please upload your images to OneDrive or DropBox and send us a link so we can investigate further.
Eric Stollnitz, Computational Photography Group, Microsoft Research