Getting below error while executing this query

Question

Please help me on this. Getting below error while executing the query.

ERROR: type "unsigned" does not exist

LINE 3: FROM_UNIXTIME((CAST(attribute_value AS UNSIGNED)/1000))

SQL state: 42704

Character: 118

Query:

SELECT d.directory_name AS "Directory", u.user_name AS "Username",
From_unixtime((Cast(attribute_value AS UNSIGNED)/1000)) AS "Last Login" 

FROM cwd_user u
JOIN cwd_directory d ON u.directory_id = d.id 
LEFT JOIN cwd_user_attributes ca ON u.id = ca.user_id 
AND ca.attribute_name = 'login.lastLoginMillis' 
WHERE u.active = 1 AND d.active = 1 AND u.lower_user_name IN 
(
    SELECT DISTINCT lower_child_name 
    FROM cwd_membership m 
    JOIN licenserolesgroup gp ON m.parent_name = gp.group_id
) 
AND
(
    u.id IN 
    ( 
        SELECT ca.user_id 
        FROM cwd_user_attributes ca 
        WHERE attribute_name = 'login.lastLoginMillis' 
        AND From_unixtime(Round(ca.attribute_value/1000))
            <= (CURRENT_DATE - interval '6 month')
    )
    OR u.id NOT IN 
    ( 
        SELECT ca.user_id 
        FROM cwd_user_attributes ca 
        WHERE attribute_name = 'login.lastLoginMillis'
    )
) 
ORDER BY "Last Login" DESC;