Problem with the dynamic checkboxes bound inside the checkboxlist placed inside the update panel

Hi,

I have a mulitselect dropdown usercontrol used in another user control five times which are all placed in a single update panel, as per the requirement when the first control is selected, based on its selection the next multiselect dropdown should populate, similarly the selection in second should populate the third one and so on.

The problem is, I can select a checkbox and populate the dropdown, but I couldnt uncheck the selected checkboxes, once the checkbox is seleted its selection property becomes true then later even if it is unchecked the property still remains true. Tried in both c# and javascript but no luck.

Multiselectdropdown.ascx

<div id="divCheckBox" runat="server" align="left">

    <asp:Panel ID="pnlMain" runat="server">

        <table id="MSDDLB_tbl" style="border-right: #b6b7bc 1px solid; table-layout: fixed;

            border-top: #b6b7bc 1px solid; border-left: #b6b7bc 1px solid; border-bottom: #b6b7bc 1px solid;

            height: 19px" cellspacing="0" cellpadding="0" width="164px" border="0" runat="server">

            <tr id="rowDD" style="height: 19px" runat="server">

                <td id="colDDTextBox" style="height: 19px; vertical-align: text-top; background-color=#e5f5fa;">

                    <asp:TextBox ID="txtCombo" runat="server" Style="cursor: default; vertical-align: middle;

                        padding-left: 5px; padding-bottom: 5px;" Width="143px" ReadOnly="True" ToolTip=""

                        Font-Size="8pt" BorderWidth="0" BorderStyle="None" Height="19px"></asp:TextBox>

                </td>

                <td id="colDDImage" style="padding-right: 0px; padding-left: 0px; vertical-align: middle;

                    padding-bottom: 0px; padding-top: 8px; height: 6px; background-repeat: no-repeat;

                    background-image: url('/Pages/Images/dropdown_arrow.gif');" width="19" runat="server">

                </td>

            </tr>

        </table>

        <cc1:PopupControlExtender ID="PopupControlExtender111" runat="server" TargetControlID="MSDDLB_tbl"

            PopupControlID="pnlCheckBox" Position="Bottom">

        </cc1:PopupControlExtender>

        <input type="hidden" name="hidVal" id="hidVal" runat="server" />

        <asp:Panel ID="pnlCheckBox" runat="server" ScrollBars="Vertical" Width="160px" Height="150px"

            BackColor="white" BorderColor="Gray" BorderWidth="1" Style="display: none;">

            <asp:CheckBoxList ID="chkList" Font-Size="8pt" Font-Names="Tahoma" runat="server"

                OnSelectedIndexChanged="chkList_SelectedChange" AutoPostBack="true">

            </asp:CheckBoxList>           

        </asp:Panel>

    </asp:Panel>

</div>

Please help.