It's because yo're providing Product and Admin. Because of Rails
recent conversion to REST, the scaffold generator only generates
controllers based on the model name, in this case you'd have
Product/ProductsController. The reason it's saying the arguments are
wrong is because it thinks Admin is supposed to be a field and you
didn't provide a type.
Also, you can leave the sizes off I think. At least, OSX didn't like
them being on there.