Load Chapter 50 and continue with the game as you normaly would, until you get the second box up the the other room.
After you did that, dont stack it on the other box, but drag it to the right of the room, get on top of it, start it and push the red button.
Wait until the wall is completly down and repeat the previous step, push the button and stand on top of the wall going up to get to the room for the achievement.