model inheritance

Hi,

I am extending a 3rd party model in my application, using multi-table inheritance. I can create an instance and modify it, but when I try to list the created objects at http://localhost:8000/en/admin/news/news/ , I am getting a nice exception:

Traceback:
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/core/handlers/base.py" in get_response
  140.                     response = response.render()
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/template/response.py" in render
  105.             self.content = self.rendered_content
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/template/response.py" in rendered_content
  82.         content = template.render(context)
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/template/base.py" in render
  140.             return self._render(context)
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/template/base.py" in _render
  134.         return self.nodelist.render(context)
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/template/base.py" in render
  830.                 bit = self.render_node(node, context)
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/template/debug.py" in render_node
  74.             return node.render(context)
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/template/loader_tags.py" in render
  124.         return compiled_parent._render(context)
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/template/base.py" in _render
  134.         return self.nodelist.render(context)
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/template/base.py" in render
  830.                 bit = self.render_node(node, context)
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/template/debug.py" in render_node
  74.             return node.render(context)
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/template/loader_tags.py" in render
  124.         return compiled_parent._render(context)
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/template/base.py" in _render
  134.         return self.nodelist.render(context)
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/template/base.py" in render
  830.                 bit = self.render_node(node, context)
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/template/debug.py" in render_node
  74.             return node.render(context)
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/template/loader_tags.py" in render
  63.             result = block.nodelist.render(context)
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/template/base.py" in render
  830.                 bit = self.render_node(node, context)
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/template/debug.py" in render_node
  74.             return node.render(context)
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/template/loader_tags.py" in render
  63.             result = block.nodelist.render(context)
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/template/base.py" in render
  830.                 bit = self.render_node(node, context)
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/template/debug.py" in render_node
  74.             return node.render(context)
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/template/base.py" in render
  1185.                     _dict = func(*resolved_args, **resolved_kwargs)
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/contrib/admin/templatetags/admin_list.py" in result_list
  286.             'results': list(results(cl))}
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/contrib/admin/templatetags/admin_list.py" in results
  264.             yield ResultList(None, items_for_result(cl, res, None))
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/contrib/admin/templatetags/admin_list.py" in __init__
  256.         super(ResultList, self).__init__(*items)
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/contrib/admin/templatetags/admin_list.py" in items_for_result
  219.             url = cl.url_for_result(result)
File "/home/roberto/.virtualenvs/ve_news/local/lib/python2.7/site-packages/django/contrib/admin/views/main.py" in url_for_result
  380.         pk = getattr(result, self.pk_attname)

Exception Type: AttributeError at /en/admin/news/news/
Exception Value: 'News' object has no attribute 'news_ptr_id'

My News model is extending another model using multiple table inheritance.

class News(OldNews):
    departments = models.ManyToManyField(Department, blank=True, related_name='news')
    objects = models.Manager()
    class Meta:
        verbose_name_plural = _('news')
        ordering = ('-pub_date', )

I can't understand the reason for this error. Can anyone enlighten me please?

Roberto