When I enter the trade screen with an AI, the Cities tab is always grayed out. The message that I get is, "The AI has no tradeable cities, or you do not have an embassy.", when I do have an embassy, and it very much looks like they have cities that should be up for trade. I'm playing on version 4.16.2 of VP. Does anyone know if this is a glitch or if I am misunderstanding what conditions make a city tradeable?