Learning Mastery Gradebook will not load when I open it

[zoeanne_soon]

Learning Mastery Gradebook will not load when I open it - there is only a spinning wheel. The traditional Gradebook view loads fine. Any ideas how to fix it so the Learning Mastery Gradebook view loads?

I have already tried clearing history and cache.  There is only a spinning wheel, when I try to open Learning Mastery Gradebook for my class to view student progress. 

Any ideas how to fix this?  Thanks so much!