When changing between aggregation methods the course total will start to display inaccurate totals. Continual changing of the aggregation method will result in the course total becoming zero.
There seems to be no way or reseting the course total or over writing it.

1. Make sure that you have a course with at least three assessments in it.
2. Go to [Course administration->Grades] and over ride a students grades to something (in QA there were four assessments with grades of 1,5,10,0 with the maximum total for each being 10).
3. Go to "Categories and items" and select full view.
4. Change the aggregation to something different, then go to "view" and check out the course total. (The first time should work fine)
5. Go back to "Categories and items" and change the aggregation again and then go back to "View" and check again. (The course total should be a wrong figure.
6. Go back and forth changing the aggregation method and you will reach a point where the course total will become 0.

Manually over ridding the total in the "view" page will not change the course total.