See: http://devilry.readthedocs.org/en/latest/releasenotes-1.3.html
BACKUP. YOUR. DATABASE. AND. FILES.
Add the DEVILRY_NOT_RELATEDSTUDENT_ON_PERIOD_URL to your /etc/devilry/devilry_prod_settings.py:
DEVILRY_NOT_RELATEDSTUDENT_ON_PERIOD_URL = "http://example.com/guides/notrelatedstudent.html"
The setting must point to a page where users can read about what do do when they are registered on an assignment, but not on the course. See https://github.com/devilry/devilry-django/issues/433 for more information about the problem, and screenshots that illustrate how users interract with this setting.
Update REVISION to v1.3 using the instructions in the update guide.