ERROR 1242 (21000): Subquery returns more than 1 row

INSERT INTO `mydb`.`service_request` (  `id_z`,  `id_app`,  `request_time`,  `priority` )

(  SELECT sc.`id_z`,         sc.`id_app`,         NOW(),         0 

   FROM `mydb`.`service_connection` sc 

   JOIN `mydb`.`service` s ON ( s.`id_service` = sc.`id_service` ) 

   WHERE 1=1   

   AND sc.`id_app` = _utf8'afr'   

   AND s.`status` = 'available'   

   AND (  sc.`last_synchronized_time` < SUBDATE( NOW(), INTERVAL 600 SECOND )  OR sc.`last_synchronized_time` IS NULL )   

   AND sc.`nb_errors` < 2  

   AND sc.`id_z` NOT IN (

             SELECT sr.`id_z`

             FROM `mydb`.`service_request` sr

             WHERE sr.`id_app` = _utf8'afr'

             AND sr.`status` IN ( 'waiting thu', 'waiting sez', 'in progress' )

           )

 ) ;