sql help

[vizagpower]

im trying to update a table based on the below logic , 

but its failing , any idea where im going wrong ??

 

UPDATE  uaimage_test
SET    imagegen_flag = ( CASE
                 WHEN datediff(SS,frr.dateEnd,ua.imagegen_dt) <= 120 THEN 0
                 ELSE 1
               END )
FROM   uas.fileread_files ff 
inner join uaimage_test ua  on ff.individual_id=ua.ind_no
inner join uas.fileread_reads frr on frr.ff_id=ff.id   
where  docType='RDST' and frr.dateEnd is not null 
and ff.id in ( select id from uas.fileread_files where lu_semester=48)