MDL-49418 reported a similar problem for a restricted access module with 2 or more activity completion requirements. It was fixed for 2.7.7 but not however fixed for glossaries. Teachers (who have not completed the 2+ activities required by the restrict access in a section/topic module) receive this error message when attempting to open a glossary in the restricted section:

"Coding error detected, it must be fixed by a programmer: The theme has already been set up for this page ready for output. Therefore, you can no longer change the theme, or anything that might affect what the current theme is, for example, the course."

Students, who can only see the glossary after having completed restrict access conditions, don't have a problem. Triage: If the teacher goes to student view and completes the required activities, glossary can then be opened in teacher's normal view. If the number of activity requirements is changed to 1, then the teacher can also get access.

How to replicate this problem in Moodle 2.7.8 (Build: 20150511):
1. login a teacher account
2. In a course, enable completion tracking
3. create two activities or resources with completion tracking conditions (ie student can manually mark, or create conditions.)
4. In a different section, edit the section summary and restrict access with activity completion of the two above activities/resources
5. Create an glossary in the restricted access section. Save.
6. Click on the glossary to open.
7. error appears where one would expect to be able to view the glossary.
8. go to student view
9. verify student cannot see the glossary or other items in the restricted section.
10. complete the two required activities or resources
11. verity student can now see and open the glossary
12 return to normal view
13. click the glossary to open
14. now glossary opens as expected, no error

This might affect other versions fixed by MDL-49418. I tested with quizzes, forums, files, books and lessons in the restricted section and they don't have an error when opening, only glossaries.