[Answer]-Adding a ManyToManyField to an existing model with django/south give me an error

Thanks to Thomas Orozco, I did find my mistake !
This line was not correct :

network = models.ManyToManyField('selfcare.apps.auth.models.Network')

I correct it like that :

network = models.ManyToManyField('auth.Network')

Then the migration did work with south !