TextBox_TextChanged(object sender, EventArgs e) event not firing when I type text into a texbox

I have a web form with a texbox control on it. When someone types a character into the textbox,
I want the TextBox_TextChanged(object sender, EventArgs e) event to be fired.

It will work if the mouse cursor is moved to a different control on the web form(Focus change).
But it will not work if someone types a character into the textbox control. Can someone tell me
how I can get the  TextBox_TextChanged event to fire when someone types a character into the
text box?
Below is the code I am using. In one text box I am using Ajax. In the other textbox I am not.
 
 
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="StringManipulation.aspx.cs" Inherits="StringManipulation" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD ...