Error adding notes

I am unable to add notes to my ebook. It is already added to my library, and I have already added a handful of notes. Mid-edit, the feature went away though. Is there a limit to the number of notes you can add (I'm only on note #5)? Do I need to restart Adobe, and if so how do I do that? When I exit Adobe and open it again, it opens to the same place I left off.