I think the terminology that's familiar to many LW readers calls "problems", "goals", and "tasks", "subgoals". Framing it that way, there isn't a difference between tasks and problems as such - a task/subgoal is merely what you get when you break down the problem/goal to smaller parts.

It seems to me you can move between the two framings by simply changing the way you describe the top-level objectives. If the top-level objectives are undesirable things that you want to change, they're problems. If they're desirable things you want to see happen, they're goals.