Problem with foreign key between 3 tables. (PgAdminIII)

I'm using pgAdmin III for PostgreSQL but I have a problem with foreign keys between 3 tables. My tables are: **Locale** with a **primary key IDnegozio** (integer type, no need to make it serial type) **Orario** with a **primary key IDorario** (integer type, no need to make it serial type) **OrarioToLocale** with two columns: **IDlocaleT** & **IDorarioT** (both integer). I'm trying to make a foreign key between IDlocale -> IDlocaleT and IDorario -> IDorarioT so, I can have the relation that a Shop can have multiples time. The problem is that when I try to make these foreign keys, and an error occurs me: "no unique constraint matching is given keys for referenced table" and I don't understand why. I tried to google but I didn't find any answer! How can I do? This is the code of the three tables: CREATE TABLE public."Locale" ( "IDnegozio" integer NOT NULL DEFAULT nextval('"Locale_IDnegozio_seq"'::regclass), CONSTRAINT "Locale_pkey" PRIMARY KEY ("IDnegozio"), ) CREATE TABLE public."Orario" ( "IDorario" integer NOT NULL DEFAULT nextval('"Orario_IDorario_seq"'::regclass), CONSTRAINT "Orario_pkey" PRIMARY KEY ("IDorario") ) CREATE TABLE public."OrarioToLocale" ( "IDlocaleT" integer NOT NULL, "IDorarioT" integer NOT NULL ) How can I do? Thank you advice!