Just a thought, as I have had this issue with a couple addons.
When you extracted it, what was the folder layout? I have extracted some addons that still have the /Interface/Addons/<Addon Folder> layout. Thus your actual Addon ends up being a couple layers farther down than what it should be (i.e. - Interface/Addons/Interface/Addons/<Addone Folder>).
I just offer this up since it has happened to me.