When I tried to change the wallpaper of my Mac mini, the cursor changed to balloon and was rotating and rotating and rotating and it was never ending. The worst thing is I cannot make any change to the ‘Desktop and Screensaver’ section of the preferences. But I managed to get back normal behavior by doing the following.
- go to /Users/<my_user_name>/Library/Preferences
- move the 3 files com.apple.desktop.plist, com.apple.systempreferences.plist, com.apple.screensaver.plist to desktop
- restart the Mac
- after restart, my ‘Desktop and Screensaver’ is functioning again
Dot ... 
Thanks for the tip—–it worked
it did not work for me…. 😦 thanks anyway..
didn’t work for me either.