Found this error while testing
Unable to restoring to 2.x from 1.9 course backup file with the following setting:
Enabling module security and preventing teachers from adding the disallowed modules.
1. Using a Moodle 1.9 site, turn on the Module security feature, and set it to restrict modules for all courses, with a default list.
2. Go into a course in this site, go to the course settings, make sure module security is turned on there, and that the list of allowed modules is right, then Save the form.
3. Backup this course, and restore it into your Moodle 2.3 dev install. Verify that role overrides are created to prevent Teachers from adding the disallowed modules.