Problem with Blender 2.62 during render with alt + d comand

Hi guys, coud you help me? I just started with blender 2.62 and to begin with I chose the present box tutorial from Cg cookie. When it comes to the part of creating the box ribbon I faced a problem with the command alt + d when I tried to render the scene.

Let me explain. I added a plain and used the subdivision surface and solidify modifiers to create the ribbon around the box and created a duplicate with the command ALT + D so the modifications I make to one modify the other as well after that I rotated the duplicate 90 degrees to cross with the original.

The problem comes when I try to render the scene, when that happens the original ribbon simply moves to the same location of the duplicate, in other words it gets over the duplicate. It looks to happen only when I apply these modifiers.

The link to the tutorial I’m using: