Couldn't figure out a simple AJAX error...need advice.

 I have a simple method in my default.aspx.cs
   [WebMethod]
    public static string sayHello()
    {
        return "hello ";
    }
I am trying to make a simple AJAX call to this method but just does not work and keep on giving me 500 interal error.
Will appreciate if someone can solve this.

This is my simple default.aspx  file.
<html>
<head>
    <title>Calling a page method with jQuery</title>

    <script src="jquery-1.2.6.js" type="text/javascript"></script>

    <script type="text/javascript">
        $(document).ready(function() {
            $("#But ...