Jquery error, Object does not support property or method.

I have two laptops with Visual Studio 2010 on them. I have a small asp.new web project on both machines that use the very same code. On one machine the code works perfectly with a popup calendar control. However on the other laprop when I run the application, I get a dialog box giving me the following error message : "Error: Object doesn't support property or method 'date' picker". I have spent a few hours trying to figure out what is wrong here, and I can't figure out why the code does not work on the other laptop. Can someone try this code out, and let me know if you are getting the same error message about the JQuery? I have attached a master page where the JQuery code is defined. Below is an asp.net page that has the textbox control used for the popup calendar.

<%@ Page Title="Home Page" Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true"
    CodeFile="Default.aspx.cs" Inherits="_Default" %>

<asp:Content ID="HeaderContent" runat="server" ContentPlaceHolderID="HeadContent">
</asp:Content>
<asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent">

                <asp:TextBox ID="txtContactDate" runat="server" class="textfield" Width="134px" 
                    style="margin-left: 0px; margin-bottom: 0px;"></asp:TextBox>
    <h2>
        Welcome to ASP.NET!
    </h2>
    <p>
        To learn more about ASP.NET visit <a href="http://www.asp.net" title="ASP.NET Website">www.asp.net</a>.
    </p>
    <p>
        You can also find <a href="http://go.microsoft.com/fwlink/?LinkID=152368&amp;clcid=0x409"
            title="MSDN ASP.NET Docs">documentation on ASP.NET at MSDN</a>.
    </p>
</asp:Content>

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MasterPage.txt