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.