Lucifer the Undying

Hi all, I've just recently purchased the game and playing through the first campaign game in Dread Lords, and have come across a problem - I can't get past the Mission "Achilles Heel" in which you need to conquer the Dread Lords underdeveloped planet. I am finding it near impossible to achieve. If I expand quickly and capture several planets before my AI allies, then the dread lords manage to take them eventually, and if the AI allies capture them similar things may occur and I don't ha