title: Django admin custom inline fails with "Please Correct the Error Below"
body: <p>I have a model class where i am using the django admin and it has a few inline forms.  I cannot save the change form for this model.  It always complains with "Please correct the error below"  even though there is no error highlighted on the page.</p>
  
  <p>I have narrowed it down to the inline that is causing problems: HorizontalInline When i remove this one everything works.</p>
  
  <p>Here are the relevant fields of my model:</p>
  
  <pre><code>class Equipment(models.Model):
      name = models.CharField(max_length=14)
      description = models.CharField(max_length=100)
  
  class HorizontalInterface(models.Model):
      name = models.CharField(max_length=100, blank=True,)    
      us_equip = models.ForeignKey(Equipment, related_name='upstream')
      ds_equip = models.ForeignKey(Equipment, related_name='downstream')
  </code></pre>
  
  <p>Here are the relevant fields of my admin.py:</p>
  
  <pre><code>class HorizontalInlineFormSet(BaseInlineFormSet):
      def __init__(self, *args, **kwargs):
          super(HorizontalInlineFormSet, self).__init__(*args, **kwargs)
          self.queryset = HorizontalInterface.objects.filter(Q(us_equip=self.instance) | Q(ds_equip=self.instance))
  
  class HorizontalInline(admin.TabularInline):
      model = HorizontalInterface
      formset = HorizontalInlineFormSet    
      show_change_link = True
      extra = 0
      fk_name = 'us_equip'
  
  class EquipmentAdmin(admin.ModelAdmin):
      list_display = ('name', 'description')
  
  
      inlines = [        
      HorizontalInline
      ]       
  </code></pre>
  
  <p>I believe the complexity that it cannot handle is related to the fact that my horizontal interface model has two Equipment foreign keys and i would like to display all interfaces both upstream and downstream related to the equipment in question but also be able to edit them and save the equipment.</p>
  
  <p>Any ideas how i can fix the save on my equipment model?</p>
  
  <p>Thanks in advance for any help.</p>