[2005] Event handler never called.

[GlenW]

The code below works, except the lButton_Click event handler is never called when any of the ImageButtons are clicked. I've done this loads of times in 2003, what am I doing wrong in 2005?
ImageMaker.aspx is just a WebForm that BinaryWrites the applicable Image as a byte[].

protected void Page_Load(object sender, EventArgs e)
  {
    this.getThumbnails();
  }

  private void getThumbnails()
  {
    System.Web.UI.WebControls.ImageButton lButton;
    foreach (string lFile in Directory.GetFiles("C:\\Graphics\\Ethan"))
    {
      lButton = new System.Web.UI.WebControls.ImageButton();
      lButton.ID = lFile;
      lButton.ImageUrl = "ImageMaker.aspx?ImageAddress=" + lButton.ID;
      lButton.Click +=new ImageClickEventHandler(this.lButton_Click);
      this.pnlThumbnails.Controls.Add(lButton);
    }
  }

  private void lButton_Click(object sender, ImageClickEventArgs e)
  {
    ImageButton lButton = sender as ImageButton;
    this.imgMain.ImageUrl = "ImageMaker.aspx?ImageAddress=" + lButton.ID + "&ImageType=full";
    th