Please, read comments to the question and follow the link provided there.
Try this:
SELECT a.SMARTCARD,a.STB,a.AREA,a.ESTATE
FROM REPORT_CAS AS a LEFT OUTER JOIN (
SELECT SMARTCARD
FROM REPORT_IW
) AS b ON a.stb = b.stb AND a.smartcard = b.smartcard
WHERE a.smartcard BETWEEN 1303379968 AND 1303969791 AND b.stb IS NULL AND b.smartcard IS NULL