ORA-01400 when trying to insert into schema.table.ID

I have a table that stores rejected contract proposals.

CREATE TABLE "STATUS_CONTRATO" (
  "STC_ID" NUMBER NOT NULL,
  "CTB_CONTRATO" NUMBER NOT NULL,
  "STC_DATA" DATE NOT NULL,
  "STC_OBSERVACAO" VARCHAR2(200) NOT NULL,
  CONSTRAINT "STATUS_CONTRATO_PK" 
    PRIMARY KEY ( "STC_ID") 
    ENABLE 
    VALIDATE,
  CONSTRAINT "FK_CONTRATO" 
    FOREIGN KEY ( "CTB_CONTRATO")
       REFERENCES "CONTRATO" ( CTB_CONTRATO) 
       ON DELETE SET NULL 
    ENABLE 
    VALIDATE)
;

(Script generated by Visual Studio 2010)

This table has a simple Trigger, where the value of STC_ID is set:

TRIGGER "STATUS_CONTRATO_TRIGGER1"
  BEFORE
  INSERT
  ON "STATUS_CONTRATO"
  FOR EACH ROW

when (new.STC_ID = 0)
DECLARE
BEGIN 
  SELECT SEQ_STATUS_ID.NEXTVAL INTO :NEW.STC_ID FROM DUAL;
END;

SEQ_STATUS_ID is a simple sequence.

Here's my problem:

I can successfuly execute this insert in the VS2010 query window:

insert into myschema.STATUS_CONTRATO s(
  s.STC_ID, s.CTB_CONTRATO, s.STC_DATA, s.STC_OBSERVACAO
)values(
  0, 10, SYSDATE, 'Inserting by hand works'
);

But, when I try to insert using EF, I'm getting this exception:

System.Data.UpdateException: An error occurred while updating the entries. 
See the inner exception for details. ---> Oracle.DataAccess.Client.OracleException: 
ORA-01400: cannot insert NULL into ("MYSCHEMA"."STATUS_CONTRATO"."STC_ID")
ORA-06512: at line 4

I'm using this code to insert

STATUS_CONTRATO statusContrato = new STATUS_CONTRATO() {
    STC_ID = 0,
    CTB_CONTRATO = codContrato,
    STC_DATA = DateTime.Today,
    STC_OBSERVACAO = observacao
};
ent.STATUS_CONTRATO.AddObject(statusContrato);
ent.SaveChanges();

I'm using VS2010, Oracle 11g (CentOS Server), ODP.NET client 11.2.0.3.0 Production, .NET Framework 4.0, EF 4.