Problem with force and kinematic coupling

[Fabi0]

I've modeled a couple of cube with contact between them. The upper cube is forced down by a force applied to a reference point, and the rp is connected to the upper surface of a cube by a kinematic coupling. Simple, but it doesn't work!

I suppose the problem is in load, because if i use pressure instead of force everything works.

Can anyone help me?? I need to use force and not pressure