Preferences Error on IMac Yosemite 10.10.2
Solved.  

Deleted the file desktoppicture.db  located in user/library/applicationsupport/dock.  Then re-started.  This restored the default wallpaper.

Even though my previous wallpaper displayed without issue, it apparently caused a problem for the Desktop &amp; Screen Saver Prefs.  I checked the jpg and it wasn't corrupt.  

If I pick another image for my wallpaper the Prefs error returns, but at least for now everything is stable!

Many thanks to Kevin G. and Buscar for the suggestions.