Sickly succulent - what's wrong with it?

I grew three succulents from cuttings in a single container on my window sill. Two of the three grew well but one looked quite sick and grew very slowly. I thought perhaps it would do better in its own container without any competition. So I broke off most of the plant, leaving the base and roots in the old container, and planted it in a new container.

It's been about a month now and my poor succulent is not looking any better. In fact, it looks more and more like it has some disease. Can anyone identify what's wrong with it? The little spots on the leaves look very suspect