I am having exactly the same problem, can't figure it out.
I found that as well but I googled it and found how how to fix it and now it works. I think I had to change the language settings.
Try:
1. Open a document that has this problem, press Ctrl+A to select all
of the text
2. Click on Review tab | Proofing: Set Language | <choose your
language> | uncheck the "Detect language automatically" and "Do not
check spelling or grammar" boxes | Default | OK.
3. Click on Office Button | Word Options | Proofing | check the
"Check spelling as you type" and "Check grammar with spelling" boxes |
uncheck the "Hide spelling errors in this document only" and "Hide
grammar errors in this document only" boxes | OK.