good!

add_action ( 'admin_menu', 'image-mapper' );
the above line should be commented, may be the function name should be ‘image_maps_menu’,but this function has be commented by you.

or wordpress will throw an error info:

Warning: call_user_func_array() expects parameter 1 to be a valid callback, function ‘image-mapper’ not found or invalid function name in……

and,the css for the custom post type ‘image_maps’ editor ,may be has a issue.