it worked perfect, your help was very useful nicolai, thanks.
and also thanks elie-7 for asking that

ps. @elie-7
did you tried setting the wallpaper also in the "normal" way?
better: to get it working right I had to set the wallpaper from "livewallaper" (as nicolai said: slideshow>wall folder>120) and manually to each desktop. hope this could help someway