If you're using MySQL5 you need to slightly change the $print_catalog_query in line 503 of pdf_datasheet_functions.php as follows:
$print_catalog_query = tep_db_query("select p.products_id, pd.products_name, pd.products_description, p.". PDF_ALT_IMAGE .", p.products_model, p.products_price, p.products_tax_class_id, p.products_date_added, p.products_date_available, p.products_status, IF(s.status, s.specials_new_products_price, NULL) as specials_new_products_price, s.expires_date, m.manufacturers_name from " . TABLE_PRODUCTS . " p left join " . TABLE_MANUFACTURERS . " m on p.manufacturers_id = m.manufacturers_id left join " . TABLE_SPECIALS . " s on p.products_id = s.products_id, " . TABLE_PRODUCTS_DESCRIPTION . " pd where p.products_id = '" . $products_id . "' and p.products_id = pd.products_id and pd.language_id = '" . $languages_id . "'");
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