Walkthrough for the "Tribes of the East" expansion.

Can you help me understand what’s happening? In the “Hunt the Hunter” mission, the fifth mission for the Stronghold faction, I’ve cleared the entire map and am approaching Shahbida, but when I try to attack (start the battle), nothing happens. Why? The attack cursor is there, and I click to attack, but it just stands there! I’ve assembled an army twice the size of the enemy’s, and the game indicates a very low threat level – I won’t even notice if I enter the battle. However, I’m playing on Veteran difficulty, I’ve collected all the artifacts, and my hero is also well-leveled (45, 30, 20, 21). The map is clear. What should I do?