If you are using desktop version of Office 2010 with SharePoint 2013 everything works great and you can open, edit and save all day. That is until you try to install any app from Office 2013 like say SharePoint Designer 2013 because you’re thinking of building some workflows.
Apparently SharePoint 2013 sees any Office 2013 app as an indicator that the entire 2013 suite is present and gives an odd error in the browser address field (ms-word:nft|u| <URL of site>/Forms/<library name> |s| <url of site>) when you try to open an office document with the desktop apps. OWA works fine it is just an Office desktop error.
Many thanks to Dr. SharePoint’s article on the subject (The only one I could find) that identified the issue. The resolution is to install the apps in descending sequence ( if you must have both) Uninstall Office 2010, install SharePoint DEsigner 2013, then reinstall Office 2010. In my particular instance simply uninstalling SPD 2013 and running a repair on Office 2010 did the trick.