Checkboxes inside my AJAX Modal popup refuse to check/uncheck

Question

I have a modal popup I am using to get some data from the user and save back to a table. I have them pick a customer and then create checkboxes for each shipto associated with that customer. I want the user to be able the select from the shiptos and then I want to save the choices to the database. I get the list of customers and create the checkboxes but I can't for the life of me get the dang things to check. You click it and nothing happens. What am I doing wrong?? :-(

My code is as follows:

HTML:

<ajaxToolkit:ModalPopupExtender   
ID="mpeEdit"   
runat="server"  
PopupControlID="pnlPopup"   
TargetControlID="pnlPopup"   
CancelControlID="btnDlgCancel"  
BackgroundCssClass ="modalBackground"  
OnCancelScript="HidePopup  ('ctl00_Content_mpeEdit')"  />  

   <asp:Panel ID="pnlPopup" runat="server" CssClass="innerPopup"   
        style="display: none;   
        width:600px;   
        postion: absolute;  
        left: 25%;  
        top: 10%;">  
        <asp:UpdatePanel runat="server" ID="chkUpdate">  
            <ContentTemplate>  
            <p class="bodyStyle" >
                <asp:HiddenField ID="hidEditID" runat="server" /><br />
                <span class="subHeaderStyle">Edit User</span>
                <br />
                <br />
                <asp:Label ID="Label15" cssclass="bodyStyle" runat="server" width="75px" style="width:75px"><b>Customer</b></asp:Label>
                <asp:RequiredFieldValidator ID="RequiredFieldValidator9" runat="server" 
                                    Width="10px" 
                                    ControlToValidate="ddCustomer" 
                                    ErrorMessage="* Customer" 
                                    ValidationGroup="modalEdit" 
                                    cssclass="bodyAlertStyle">*</asp:RequiredFieldValidator>
                <asp:DropDownList cssclass="bodyStyle" width="400px" style="width:400px; text-align:left" ID="ddCustomer"  AutoPostBack="true" runat="server" />
          </p>
              <table>  
                    <tr>  
                        <td valign="top"><asp:Label ID="Label16" cssclass="bodyStyle" runat="server" width="92px" style="width:92px"><b>Ship Tos</b></asp:Label></td>  
                        <td valign="top">  
                            <asp:Repeater ID="rptChklstShipTo" runat="server">  
                                <ItemTemplate>   
                                    <asp:CheckBox ID="chkShipTo" AutoPostBack="true" runat="server" />  
                                    <asp:Label runat="server" CssClass="bodyStyle"><%# DataBinder.Eval(Container.DataItem,"ACCOUNTNUM")%></asp:Label>  
                                    <br />  
                                </ItemTemplate>  
                            </asp:Repeater>  
                        </td>  
                    </tr>  
                </table>  
            </ContentTemplate>  
        </asp:UpdatePanel>  
        <p align="center" class="bodyStyle">  
                <asp:Button Height="20px" CssClass="cssButtonGreen" Text="Update" ValidationGroup="modalEdit" CausesValidation="true" id="btnDlgOK" runat="server"/>  
                <asp:Button Height="20px" CssClass="cssButtonGreen" Text="Cancel" id="btnDlgCancel" runat="server"/>  
        </p>  
    </asp:Panel>

Server Side code to create checkboxes:

Private Sub FillRepeaterWithShipTos(ByVal rpt As Repeater, ByVal sCustomer As String)    
rpt.DataSource = Nothing    
Dim dtShipToList As DataTable = wcf_CustomerPortal.GetShipToList   (sCustomer, "000")     
If Not dtShipToList Is Nothing AndAlso dtShipToList.Rows.Count > 0 Then    
rpt.DataSource = dtShipToList    
rpt.DataBind()    
End If    
End Sub