$this->validatorSchema->setPostValidator(
      new sfGuardValidatorUser(
        array(
          'username_field' => 'username',
          'password_field' => 'password',
          'throw_global_error' => false
        ),
        array(
          'invalid' => 'The username and/or password is invalid.',
          'inactive' => 'Your account was suspended.'
        )
      )
    );