Can't shift-select to unselect items

I am running AutoCAD 2013, and when I shift select to unselect objects (lines, polylines, etc.) it doesn't unselect but rather a window called "Image Select" appears and asks me which image(s) I would like to select. Any idea how I can unselect items on the fly?

Thanks-

Sounds like you also have Raster Design installed... From the help:

 

Mouse Settings

+ Left-Click Image Select Enables you to select images by placing your cursor over them and holding the Shift key down while clicking your left mouse button. This feature is useful when you are zoomed in to the image and cannot see the image frame. For more information, see Selecting an Image.

 

When you activate Shift + Left-Click Image Select here, it overrides the AutoCAD Shift + Left-Click to deselect entities for pickfirst and grip editing.