when i try to construct the UDF using

DECLARE EXTERNAL FUNCTION trim
varchar(50)
RETURNS CHAR (40) FREE_IT
ENTRY_POINT 'fn_trim' MODULE_NAME 'udflib';

i could declare successfully but when i use it on insert statement
e.g.
INSERT INTO "UDF2" ("ID", "FIELD_1") VALUES (1, Trim(2,'','2 4'));
the ib-console prompt me error on module name or entrypoint could not
be found....

could anyone know how to solve it?