We had, in a 2-player game- the situation that I could not add a stone. The rules say: "If you cannot add a stone (...) you go on to the next action".
The next action says: "Take a new stone (...) to replace the one you just added." You can't have more then two stones.
So, I guess the part "you on to the next action" means "your turn is over and the next player takes his turn." Right?