Sometimes strange behavior from a WWS550i scanner can be corrected by using the reset button. This button is inside the housing.
The picture below describes how to find it: Holding the scanner with the aperture/lens pointing away from you, on the right side there is an oval hole. Insert a straightened paper clip or similar implement at the end of the hole toward the scanner lens. Press the button for about a second, then release (you will feel a click when the button is pressed). Then try scanning again.