I don't get it. Imagine there is a stick leaning aganist a wall. There is a moment couple somewhere on the stick. The end of the stick hits the wall and the wall acts against it. The sum of moment is 0 but since the moment couple forces cancel each other, the resultant force is the wall reaction force! which means the stick will move away from the wall! But in reality i think the whole structure is stationary but not this!!!!!