3065 - Expression #1 of ORDER BY clause is not in SELECT list, references column 'gajasilver_xyz.a.articles_sort_order' which is not in SELECT list; this is incompatible with DISTINCT

select distinct ax.articles_id, ad.articles_name, a.articles_photo, ad.articles_description from cms_articles_xsell ax, cms_articles a, cms_articles_description ad where ax.xsell_id = '404' and ax.articles_id = ad.articles_id and a.articles_id = ad.articles_id and ad.language_id = '1' and a.articles_status = '1' and a.articles_photo <> '' order by a.articles_sort_order asc