I set up a simple website using ajax framework. The code of html page is as below:
<!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" >
    <title>Getting XML with ReadXmlWithGet</title>

    <script type="text/javascript" src="ajaxframework.js" />

    <script type="text/javascript" >

    function callback(xml)
        xmlData = xml.getElementByTagName("data");
        document.getElementById("targetDiv").innerHTML = xmlData(0).firstChild.data;

    <h1>Getting XML with ReadXmlWithGet
        <input onclick="readXmlWithGet('data.xml', callback)" type="button" value="Display Msg 1" />
    <div id="targetDiv" height="100" width="100">The fetched data will appear here.
When I click button after running from Visual Studio 2005, I get error called "callback is undefined."
I am new to this. Anybody could tell me why?