[Edit]
Okay, I can't figure it out.
Trying to add a clock applet:
The panel encountered a problem while loading "OAFIID:GNOME_ClockApplet".Hmm, can't change my wallpaper either.
Details: Failed to resolve, or extend '!prefs_key=/apps/panel/profiles/default/applets/applet_8/prefs;background=none:;orient=down;size=x-small;locked_down=false
Do you want to delete the applet from your configuration?