piranha,

not sure in 8i, but can you try any one of the followings:

UPDATE
(
SELECT
 A.STDCOST A_STDCOST,
 B.COST B_COST
FROM
 Table_A A,
 Table_B B
WHERE
 A.ITEM = B.Item AND
 A.Location = B.Location 
)
SET
 A_STDCOST = B_COST;

(OR)

MERGE INTO Table_A A USING Table_B B
ON (A.ITEM = B.Item AND A.Location = B.Location)
WHEN MATCHED THEN A.STDCOST=B.COST ;