This is for Errata.
But anyways if you can't discover the problem here the fix.
Professional ASP.NET 2.0 Page 144 Listing 5-9 The Click event for the ImageButton control
c# and vb has the same "error"

[c# code] as shown in the book:

protected void ImageButton1_Click(object sender,System.Web.UI.WebControls.ImageClickEventArgs e)
    {
         //i was here:)
    }

//--------------------------------------------------------------------

Should be like this:

protected void ImageButton1_Click(object sender,System.Web.UI.ImageClickEventArgs e)
    {
       //Example from me...
       Response.redirect("http://p2p.wrox.com");
    }

NO need in .WebControls namespace!!!
You'll find ImageClickEventArgs under .UI namespace.