Why is dynamic spelling (or check spelling) not working on a particular document?

Question

I have a coupe documents where neither Dynamic Spelling or Spell Check are working. Both are documents where those tools have been used before successfully. These are files that have been shared via Dropbox for editing. There are however other files that have been shared and edited the same way, with the same team, where both Dynamic Spelling and Spell Check continue to work.
Documents are InDesign CS6.
I have tried moving files to my desktop as well as saving a copy, neither of which worked.
Last resort would be to make a whole new file and copy/past over all the content, but obviously I'm trying to avoid that if there is an easier solution.
Any thoughts would be helpful.
- Alice

Answer 1

Ended up having the same issue in a CC version document. A combination of fixing the Language setting on character styles and editing Preferences, Dictionary, Spelling and also Hyphenation to Hunspell did the trick.
It should be noted that both of these problem files were ones that were being shared and edited by two people via dropbox. I'm guessing that the preferences are not set correctly within InDesign by the other user, thus resulting in what you noted above as a change in the language associated with the file. A cautionary tale for anyone working with a client who may be doing some content editing on a shared file, as it seems settings overwrite.