A JOIN predicate was specified with an OUTER JOIN indicator (+). Using this OUTER JOIN indicator you can desribe a LEFT OUTER JOIN only.
Example
SELECT ... FROM table_a, table_b
WHERE table_a.column_a = table_b.column_b(+)
AND table_b.column_b = table_a.column_a(+)
If you want to use a FULL OUTER JOIN, change the SQL statement using ANSI syntax.
Example
SELECT ... FROM table_a
FULL OUTER JOIN table_b ON table_a.column_a = table_b.column_b