In the Fallen Enchantress scenario on the 3rd map (the one after you free the Oracle), your starting city "Kilford" has 0 Material, 0 Grain and 0 Essence.
This means that you cannot build, cannot increase your mana regeneration and cannot train troops.
Is this intentional? It really doesn't make sense in the flow of the scenario as it isn't explained why it would be that way.
Also it's kind of breaking gameplay.