ctr snapping faces to a vertex isn't working

I’m doing a tutorial here: http://cgcookie.com/blender/cgc-series/weapon-modeling-an-m4/#header I already used snapping in this tutorial (after getting help in this forum), but now it’s stopped working. I set the magnet to vertex snap. Then I’m supposed to extrude selected faces to a vertex by pressing ctr and hovering the cursor over the vertex. But the faces won’t snap. Can someone tell me what I am doing wrong? I tried going into vertex mode, but the selected vertexes wouldn’t snap either.

Where I am having a problem:

Link to my Blend file

http://www.pasteall.org/blend/19203

You have disabled the ‘Snap Onto Itself’ button to the right of ‘Closest’

Attachments


Thank you.
This site is great. I would have given up on blender a long time ago if it weren’t helpful people like yourself.