Why i cant save my form to my database? Many to many, django

Question

I have an issue here. I have my form with one field (many to many), this field maps to a m2m table with the atributes id_academic_degree id_employee and license. When i try to save it, django displays an error like this

Cannot set values on a ManyToManyField which specifies an intermediary model. Use employees.EmployeeAcademicDegree's Manager instead.

View

CreateEmployee(CreateView):
    model = Employee
    form_class = EmployeeForm
    template_name = 'CreateEmployee.html'

@transaction.atomic
def form_valid(self, form):
    form.save()
    form.save_m2m()
    messages.success(self.request, 'El Empleado fue guardado Exitosamente.')
    return HttpResponseRedirect(self.get_success_url())

def get_success_url(self):
    return reverse('physicians:CreatePerson',)

my model

class Employee(models.Model):
    person = models.OneToOneField(Person)
    region = models.ForeignKey(Region, db_column='id_region')
    academic_degrees = models.ManyToManyField(AcademicDegree, 
                       through='EmployeeAcademicDegree', blank=True)
    active = models.NullBooleanField()
    rfc = models.CharField(max_length=15, blank=True, null=True)
    shift_start = models.TimeField(blank=True, null=True)
    shift_end = models.TimeField(blank=True, null=True)
    history = HistoricalRecords()  # Always leave at the end.

    class Meta:
        db_table = 'employee'

    def __str__(self):
        return self.person.full_name

    def __unicode__(self):
        return self.person.full_name

class EmployeeAcademicDegree(models.Model):
    employee = models.ForeignKey(Employee, db_column='id_employee')
    academic_degree = models.ForeignKey(AcademicDegree,
                                        db_column='id_academic_degree')
    license = models.CharField(max_length=15, blank=True, null=True)
    history = HistoricalRecords()  # Always leave at the end.

    class Meta:
        db_table = 'employee_academic_degree'

    def __str__(self):
        return unicode(self.academic_degree)

    def __unicode__(self):
        return unicode(self.academic_degree)

And the tables are the following

Employee
  id
  id_person
  id_region
  active(boolean)
  rfc
  shift_start
  shift_end

employee_academic_degrees
  id_employee_academic_degrees
  id_employee(FK)
  id_academic_degree(FK)
  license

I suppose that i need to save first the relation then the whole object (but i dont know how to save the license, because the form doesnt display any field to fill the license)