Problem inserting firebird data into ubuntu

I am using firebird in Ubuntu and when performing an insert the following error appears:

  

invalid request BLR at offset 230; function STRLEN is not defined; module name or entrypoint could not be found [SQLState: HY000, ISC error code: 335544343]

Looking at the file ib_udf.sql the strlen function is already there. What can I be missing out on?

DECLARE EXTERNAL FUNCTION strlen
    CSTRING(32767) CHARACTER SET NONE
    RETURNS INTEGER BY VALUE
    ENTRY_POINT ''IB_UDF_strlen'' MODULE_NAME ''ib_udf'';

The query I'm using does not even use strlen:

  

INSERT INTO CRACHES (CODPERFIL, STATUS, QUEM_DESABILITOU, VALID, CRACHA, ULT_HABILITACAO, RETEM, QUEM_HABILITOU, ULT_DESABILITACAO, VALIDADE_INDETERMINADA)   VALUES ('1', 'D', NULL, NULL, IIF ('20101449' = '', LPAD ('2' || LPAD (1449, 7, '0')) LPD ('20101449', 16, '0')), NULL, 'N', 'CATRACA', NULL, 'S')