Validationerror [u'managementform Data Is Missing Or Has Been Tampered With'] Only In Special Cases

When editing a model field through Django Admin, I'm getting a [u'ManagementForm data is missing or has been tampered with'] validation error. Steps: Edit a model through Django A

Solution 1:

The error: [u'ManagementForm data is missing or has been tampered with'] was because the inlines doesn't appear, so the MAX_TOTAL_FORMS and others doesn't concord.

The inlines didn't appear because there were errors in __unicode__ functions from the models.

Returning unicode type (python 2) in the __unicode__ function solved the issue.