Erro em Variável em Trigger

AS
DECLARE VARIABLE MES CHAR(2);
DECLARE VARIABLE ANO CHAR(4);
DECLARE VARIABLE CORTE CHAR(2);
DECLARE VARIABLE VENC CHAR(2);
DECLARE VARIABLE DATA DATE;
DECLARE VARIABLE DTCORTE DATE;
DECLARE VARIABLE NREGISTRO SMALLINT;
BEGIN
 FOR SELECT COUNT(*) AS REGISTROS FROM TABFATURAS FT WHERE FT.NTITULAR=NEW.NCARD
 AND FT.FECHADA=0 INTO :NREGISTRO DO
 BEGIN
 IF (NREGISTRO > 0) THEN
  BEGIN
   IF (NEW.TIPO=´D´) THEN
    BEGIN
     UPDATE TABFATURAS SET DEBITO=DEBITO + NEW.VALOR WHERE NTITULAR=NEW.NCARD AND FECHADA=0;
     UPDATE TABFATURAS SET SALDOFATURA=SALDOFATURA + NEW.VALOR WHERE NTITULAR=NEW.NCARD AND FECHADA=0;
    END
     ELSE IF (NEW.TIPO=´C´) THEN
      BEGIN
       UPDATE TABFATURAS SET CREDITO=CREDITO + NEW.VALOR WHERE NTITULAR=NEW.NCARD AND FECHADA=0;
       UPDATE TABFATURAS SET SALDOFATURA=SALDOFATURA - NEW.VALOR WHERE NTITULAR=NEW.NCARD AND FECHADA=0;
     END
  END
  ELSE IF (NREGISTRO <= 0) THEN
   BEGIN
   FOR SELECT CLI.DIACORTE,CLI.DIAVENCIMENTO FROM TABCLIENTES CLI WHERE
    NCARTAO=NEW.NCARD INTO :CORTE,:VENC DO
    BEGIN
     for select extract(month from current_date) from rdb$database into :MES do
     for select extract(year from current_date) from rdb$database into :ANO do
      BEGIN
       DATA=VENC+´/´+MES+´/´+ANO;
       DTCORTE=CORTE+´/´+MES+´/´+ANO;
      END
     INSERT INTO TABFATURAS(NTITULAR,VENCIMENTO,SALDOANT,PGTOANT,SALDOREMAN,
     SALDOFATURA,PGTOMIN,PAGO,FECHADA,VRPAGO,DATAPROC,DEBITO,CREDITO,DATAPGTO)
     VALUES(NEW.NCARD,[i]DATA+30[/i],0,0,0,NEW.VALOR,0,0,0,0,[i]DTCORTE+30[/i],NEW.VALOR,0);
    END
   END
 END
END ^

ISC ERROR MESSAGE:
Dynamic SQL Error
SQL error code = -206
Column unknown
DATA
At line 40, column 23.