I have just looked up my previous quest for help in a similar problem. Sea Urchin came up with one solution. I recreate it here, because it worked at the time, and hope he doesn’t mind:
Open your Word 2010 document, and select to highlight all the text. Then on the Review tab click on Language, then Set Proofing Language. UNcheck the "Do not check spelling or grammar" box and Apply/OK etc.
However, this time when following that advice, I found that the box was still Unticked.
Is there a way to actually prevent this ?