I get this pop up message stating "Full value of stock must be credited when all stock is being removed."

I don't understand why I am getting this message when I am creating a purchase invoice to buy stock to put into my inventory.

My inventory amounts are based on price. e.g.. $10,000.00 worth of paint, $1,000.00 worth of wallpaper. I do not need to itemize it to rolls or boxes or such units.