Master page - javascript code - not running

see my master page, the  <button type="button" style="width:50px;height:23px;" value="vb"

                         onclick="redirect()">Go</button>
causes error when button is clicked?
 txtTitle is null?
any idea

 <%@ Master Language="C#" AutoEventWireup="true" CodeFile="MasterPage.master.cs" Inherits="MasterPage" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<script language="javascript">      
function redirect(){
window.location.href='SearchBook.aspx?title=' + document.ge ...