According to
the plugin docs[
^], the array that you pass as the parameter uses
parent_category_id
,
not category_group
.
Here's the example they use that you may want to follow:
<?php wpsc_start_category_query( array(
'parent_category_id' => $category_id,
'show_thumbnails' => $show_thumbnails,
'show_name' => $show_name
)
); ?>