Ranger – “Defense” [Campaign 5, Mission 3]

I don't even know what to suggest... I played through the mission three times with different patches (starting with 1.1) and didn't encounter any bugs or glitches... All the scripts worked...
As for the walkthrough, if you really don't have enough troops, try lowering the difficulty... Although, it's possible that your hero's build isn't optimal... I had one build with resurrection and all the mass spells, and another with summoning, phoenix, and celestial shield, and both of these skill sets played a crucial role in completing the mission...