i think the sequence that caused the problem went something like this: downloaded new image and put the file on the desktop. added the image to iphoto library. deleted the file from the desktop. (smart!) right-clicked on desktop and chose change desktop background. selected the image i had added to iphoto. background went blue. Now - whenever i try to change the desktop background, it freezes and then i get the "The application System Preferences unexpectedly quit" message. relaunching does no good. restarting good. help. thanks.