ERROR: UNIQUE constraint matching given keys for referenced table "rl_voltas" not found

Hi! I'm a beginer in PosrgreSQL, and I have a problem I can't resolve.

 

The script is the following :

 

CREATE TABLE RL_RefVoltas(
 NVolta SERIAL NOT NULL PRIMARY KEY, 
 Designacao VARCHAR(15) NOT NULL, 
 Tipo INT NOT NULL  
);

 

CREATE TABLE RL_Voltas(
 NVolta INT NOT NULL, 
 Data DATE NOT NULL, 
 Hora TIME NOT NULL,
 Matricula VARCHAR(9),
 NLitros INT,
 PRIMARY KEY (Data,Hora),
 foreign key (NVolta)references RL_RefVoltas(NVolta)
);

 

CREATE TABLE RL_Cisterna(
 NVolta INT NOT NULL,
 Data DATE NOT NULL, 
 Hora TIME NOT NULL, 
 NCist INT NOT NULL PRIMARY KEY, /*1 a 4*/
 Acidez INT, 
 ProvaAlcool BOOL,
 TFermentacao TIME,
 Fermentacao FLOAT,
 foreign key (NVolta, Data, Hora) references RL_Voltas(NVolta, Data, Hora)
);

 

The result of executing this script is :

 

ERROR:  UNIQUE constraint matching given keys for referenced table "rl_voltas" not found

 

Anybody can tell me why?

 

Thanks, and good work.