Fix: Run a repair of Office 2007 Enterprise. (If you have OneNote installed separately, repair OneNote.) When I ran this, the problem immediately was fixed. Based on this fix, I have to assume that some file in OneNote 2007 got corrupted when the OneNote Windows app hung. In recalling how I got to this broken state, it made sense. I suppose that’s the hazard of constantly fixing stuff. Sometimes your own problems get lost in the shuffle.