Comment 5 for bug 1197075

Could you please try if using this command in a terminal will change the wallpaper:

kwriteconfig --file plasma-appletsrc --group Containments --group 1 --group Wallpaper --group image --key wallpaper <path-to-wallpaper>

Replace <path-to-wallpaper> with the full path to some image, or also try with "file:///path_to_some_image".

This is from this thread: http://ubuntuforums.org/showthread.php?t=803417&page=2

Thanks.