Definition of TEXT_NO_PRODUCTS is missing from
/includes/languages/english/specials.php and /includes/languages/english/featured_products.php

On a fresh install with no featured products I got TEXT_NO_PRODUCTS as the page heading.

Adding the following line to specials.php and featured_products.php fixed the issue

define('TEXT_NO_PRODUCTS', 'There are no products to list in this category.');