Exception from Word.ApplicationClass.Activedocument all of a sudden

Question

I have this single line of code in a Word VSTO add-in project which used to work but suddenly doesn\'t anymore:

Microsoft.Office.Interop.Word.Document doc =          


        

Answer 1

Well, rolling back to the previous version of Windows 10 (1803 in my case, apparently) fixed the issue, and I can't reproduce it at the moment, so I'll mark this as solved for now.

While I still have no clue what exactly the deal was, I did at least learn in my research that clicking the "Check for updates" button in Windows 10 instantly makes you a beta tester for Microsoft. As in, they deliberately put you on the unstable update train, without any sort of notice, let alone a warning that you're about to install updates that they don't consider ready for release yet.

Anyway, I hope they got some good telemetry from my many, many hours of trying everything I could think of, so that maybe the issue is fixed by the time the update is forced on me. If not, I guess I'll be back to ask the same question again. At least I'll know where to start looking for the cause.