1191 - Can't find FULLTEXT index matching the column list

SELECT click_modifier, current_clicks_theme + (current_clicks/20) AS current_clicks, click_modifier * (current_clicks_theme + (current_clicks/20)) AS clicks_count, product_id, merchant_id, sale_date, programname, name, description, sku, imageurl, buyurl, price, retailprice, add_date, promotionaltext, affiliate_product_id, feed_source, feed_source_alt, relevance_modifier, priority, gender, num_sale_reduction, manufacturer FROM product WHERE MATCH(themes) AGAINST ('Mother_of_the_Bride_Shoes') AND use_in_theme=1 GROUP BY product_id ORDER BY clicks_count DESC, priority DESC, relevance_modifier DESC LIMIT 0, 64