ManyToMany DoesNotExist exception when saving in the admin interface

[sandro]

I have these models:

class Attachment(models.Model):
  file = models.FileField(upload_to="attachments",null=True)
  ...

class Announcement(models.Model):
  ...
  attachments = models.ManyToManyField(Attachment,blank=True)
  ...

When I Add a new announcement in the django admin and hit 'Save' I am
brought to an error page that says:

DoesNotExist at /admin/student_update/announcement/add/
Attachment does not exist for {'pk': None}

  Request Method:  POST
  Request URL:  http://djanghost.mine.nu:8001/admin/student_update/announcement/add/
  Exception Type:  DoesNotExist
  Exception Value:  Attachment does not exist for {'pk': None}
  Exception Location:  /home/santuri/magic-removal/django/db/models/query.py in get, line 191 

The announcement does save, I just get this nasty error message as my POST response.

[Simon G. <dev@…>]

I'm marking this as worksforme, as I'm unable to confirm this on a current svn, adding something to the announcements does not give any errors. If anyone else is having this issue, please reopen this ticket and provide more information.