http://pastebin.com/K4wRuK44 this is the code
and this is the error
this is the line with error
leftWall.center = new Vector2(mainCam.ScreenToWorldPoint (new Vector3 (0f, 0f, 0f)).x – 0.5f);
Welcome to the wonderful world of debugging!
I suggest you revisit the tutorial and figure this one out solo.
You’re only going to learn through trial and error, so others doing it for you is counterproductive.
Give it another couple of goes, it’s undoubably the simplest thing.
Use the error as a clue as to what you need to check.