Originally Posted by DarkScribe
If you take the commas out and use en or em dashes it will accept it because the construction - although still clumsy - is now valid.
Depends upon whose grammar you're using, I guess. The only one I can remember dashes being taught at all was the hyphen, which had a caveat that you should use as few as possible. AKA none.
This was repeated in the 1996 Little,Brown Handbook (which I took great pleasure in burning when I got out of high school). No dashes, just hyphens. Parentheses were also right out, because the MLA has reserved them for parenthetical citation.
Either way, IMO the Word grammar checker just doesn't like complex sentences.