I am new on Django, I am using Django 1.6.1 and in one of my form I get the next error 

```
 This field is required.

```

I don't understand why I get this error, my form is very basic, so my Model, the statement who launch this error is form.is\_valid(), but I don't know why. 
Some help would be apreciate.

my views is:

```
if request.method == 'POST':
    form = campoImagenForm(request.POST, request.FILES)
    if form.is_valid():
        articulo = form.save(commit=False)
        articulo.item = item
        articulo.atributo = atributo
        articulo.save()
        return HttpResponseRedirect('/workproject/' + str(project.id))

```

my Form is:

```
class campoImagenForm(forms.ModelForm):
    class Meta:
        model = campoImagen
        fields = ('imagen',)

```

my Model is: 

```
class campoImagen(models.Model):
    item = models.ForeignKey(ItemBase)
    atributo = models.ForeignKey(TipoItem)
    imagen = models.ImageField(verbose_name='Imagen', upload_to='archivos')
    version = models.IntegerField()

```

I don't have a clue of why I get such an error.