The pulldown boxes in the right-hand sidebar of the admin area are built from a function named zen_cfg_select_drop_down().
NOWHERE does Zen Cart call the function by SHOPNAME_zen_cfg_select_drop_down()

So, that suggests that whoever set up the site or wrote addons or customizations for it has made an error in one or more of the set_function fields of the product_types_layout table, which is where the calls to such a function are stored as it relates to product types.