The document contains an image map that is server-side instead of client-side.
Server-side image maps are not keyboard accessible; mouse clicks are required to access the links contained in the image, making the image inaccessible to people who only use keyboards for their navigation.
Server side image maps pass the coordinates of the mouse click to the server-side script used to process the image map. Because they rely on mouse clicks, they are not keyboard accessible, whereas client-side image maps are keyboard accessible. Further, it is not possible to provide text alternatives to the actionable areas of a server-side image map like you can with the areas of a client-side image map.