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 piezas
FOR 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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