cache lookup failed ???? What is it ???!!!

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I can't execute this SQL query:  DELETE FROM piezas WHERE ord_mec = '01-001'
I get:  ERROR: fmgr_info: function 39816: cache lookup failed

Can someone help me with this error ??

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CREATE TABLE piezas (
n_pieza        INTEGER PRIMARY KEY,n_material    INTEGER NOT NULL,ord_mec    VARCHAR(8) NOT NULL,
t_inicio                TIMESTAMP DEFAULT 'invalid',t_final        TIMESTAMP DEFAULT 'invalid',
ref_eisenor    VARCHAR(32),ref_cliente    VARCHAR(32),           n_plano        VARCHAR(32),
n_lote        VARCHAR(8),
observaciones    VARCHAR(256),
FOREIGN KEY (n_material) REFERENCES materia_prima(n_material),FOREIGN KEY (ord_mec) REFERENCES ord_mecanizado(ord_mec)
);


CREATE TABLE materia_prima (
n_material    INTEGER PRIMARY KEY,fecha        DATE NOT NULL DEFAULT 'today',n_albaran    INTEGER,n_pedido_mp
INTEGER,n_lote       VARCHAR(8),
 
cantidad    INTEGER,usadas        INTEGER DEFAULT '0' CHECK (usadas>=0 AND usadas<=cantidad),torcidas_plano    INTEGER
DEFAULT'0' CHECK (torcidas_plano>=0 AND 
 
torcidas_plano<=cantidad),torcidas_canto    INTEGER DEFAULT '0' CHECK (torcidas_canto>=0 AND 
torcidas_canto<=cantidad),
dim_ancho    FLOAT,dim_alto    FLOAT,dim_largo    FLOAT,material    VARCHAR(32),pc_C        FLOAT,
observaciones    VARCHAR(256)

);


CREATE FUNCTION materia_prima_release_one() RETURNS OPAQUE AS 'BEGIN UPDATE materia_prima SET usadas=usadas-1 WHERE
n_material= OLD.n_material; RETURN OLD;END;'
 
LANGUAGE 'plpgsql';

CREATE TRIGGER piezas_delete AFTER DELETE ON piezasFOR EACH ROW EXECUTE PROCEDURE materia_prima_release_one();


- -- 
Fernando Moyano

Frase del día:
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Si las mujeres fueran buenas, Dios tendria una.

(*) SymeX ==> http://symex.lantik.com
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