codice:
 1   SELECT 
 2   pts.userid, 
 3   pts.points, 
 4   com.value
 5   FROM (
 6          SELECT 
 7          c.value, 
 8          MAX(p.points) AS max_pts
 9          FROM  k6l0c_community_fields_values AS c
10          WHERE c.value=16
11          INNER JOIN  k6l0c_alpha_userpoints AS p     ON p.userid = c.user_id   
12          INNER JOIN  k6l0c_user_usergroup_map AS grp ON c.user_id = grp.user_id  
13          WHERE grp.group_id = 2
14          GROUP BY c.value ) AS sub
15   INNER JOIN  k6l0c_community_fields_values AS com ON com.value = sub.value     
16   INNER JOIN  k6l0c_alpha_userpoints AS pts        ON pts.points = sub.max_pts AND pts.userid = com.id
17   INNER JOIN  k6l0c_users AS usr                   ON usr.id = pts.userid  
18   WHERE com.value!='' AND pts.points >0
19   ORDER BY pts.points DESC
ciao,

non vorrei sbagliare ma a me sembra che ci sono 2 where al rigo 10 e al rigo 13.
credo sia quello l'errore, il where deve andare dopo INNER JOIN che sta al rigo 12

facci sapere.
ciao