Registry Policy Setting--MS Word Problem

Hello to all.

I am trying to open an MS Word document.  I got a window that said "You are attempting to open a file that was created in an earlier version of Microsoft Office (a true statement but that hasn't been a problem before). This file type is blocked from opening in this version by your regisrty policy settings." 

It appears to be a selective denial, with some 'older' documents opening in a normal manner, and others giving me this error message. What's this all about and how do I open up this file, and other 'older' files?  This hasn't been a problem before.  What are registry policy settings and how do I modify them?

Thanks for any help and education.