850pp means that you've worked on this document over a period of time. Yes? Anyway, what I have not seen in this thread is whether you have tried "Save as" with a new document name to force out the gremlins. Also, the link to the Office for Mac forum thread that rccharles provided bears attention, especially the last post by John McGhie, who suggested a number of solutions one being "The Maggie" that rccharles also noted.
Anything such as a space, font, paragraph or line break and etc. could be the culprit. You mentioned that you are now working or have open one document at a time. Your "Normal" template could be corrupt. To make a new Normal template, quit all Office applications. Locate the current one at
~/Documents/Microsoft User Data/Normal
Name the Normal template something else such as xNormal, oldNormal
Launch MS Word and it will automatically create a new Normal template. You may need to reset your Preferences. Test with new and old documents, saving, quiting etc. It everything works then you can trash your old Normal template document.
HTH