Could you search the file:
/includes/functions/functions_lookups.php

And find the function that starts with:
Code:
  function zen_get_products_category_id($products_id) {
and paste the contents here ...

Also look for the function:
/admin/includes/functions/general.php

and find the function that starts with:
Code:
  function zen_get_products_category_id($products_id) {
and paste it here as well ...