Our apologies. "salesgenrecode" has nothing to do with "genres" and will be removed in the next API release. Please don't use it.
In the Y! Music world, we have "categories". Categories can be genres, eras, themes, etc. So just specify a "response=categories" parameter to get associated categories for something. i.e. us.music.yahooapis.com/artist/v1/item/256352;response=categories
Scott