Even a description of what is not working would help. When I use IK, if I move a hand, the arm moves all the way to the shoulder. If I move a foot the leg moves all the way to the hip. Dan Ebbert's expressions keep the limbs moving in the right direction so the joints act normal. Without the expression you can easily get into a situation where if you move a foot the knee bends the wrong way. From your explanation of the problem I can assume that the foot detaches from the lower leg or the knee bends the wrong way, or the foot an shin detach from the thigh, or the thigh detaches form the hip...
It would take you about a half hour to set up your comp with Dan's expressions. Just read carefully and your puppet would work perfectly.