Error when I use a search button

 I have created a search button as a user control.
Here's the code :
SearchBox.ascx.cs :
 
using System;
using System.Collections.Generic;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class UserControls_SearchBox : System.Web.UI.UserControl
{
protected void Page_Load(object sender, EventArgs e)
{
//don't populate control on postbacks
if (!IsPostBack)
{
//tie the search text box to the Go button
Utilities.TieButton(this.Page, searchTextBox, goButton);
//load se ...