My linkbutton won't postback

For some reason which eludes me, the link button LinkButton_cloneSequence, invokes the modal popup but when I hit the OK button in the modal popup, it doesn't call back to the codebehind.
I have the same thing in other places in my code, and there it works, but with the link button, something is wrong and I can't figure it out.

Thanks

<div id="availableJobSequences" class="availableJobSequences">
        <asp:UpdatePanel ID="UpdatePanel_hoverMenu" runat="server">
            <ContentTemplate>
         <asp:LinkButton ID="LinkButton_cloneSequence" runat="server" CssClass="sectionSubText"
                    CommandName="clone" CommandArgument="none" onCommand="LinkButton_cloneSequence_Click"  Text="Clone" />
                <cc1:ModalPopupExtender ID="LinkButton_cloneSequence_ModalPopupExtender" PopupControlID="panel_sequenceClone"
                    DropShadow="true" runat="server" Enabled="True" BackgroundCssClass="modalBackground"
                    RepositionMode="RepositionOnWindowResizeAndScroll" TargetControlID="LinkButton_cloneSequence"
                    CancelControlID="Cancel_Button" OkControlID="Clone_Button">
                </cc1:ModalPopupExtender>
                <asp:Panel ID="panel_sequenceClone" runat="server" CssClass="modalPopup" Width="300px"
                    EnableTheming="False" EnableViewState="False">
                    Are you sure you wish to clone the sequence
                    <br />
                    <font color="#FF0000"><b>
                        <asp:Label ID="Label_seqToClone" runat="server" Text='<%# String.Format("{0}", Eval("actionSequenceName"))%>' /></b></font><br />
                    <br />
                    <div align="center">
                        <asp:Button ID="Clone_Button" CssClass="modalPopupButton" runat="server" Text="Clone Sequence Step" />
                        <asp:Button ID="Cancel_Button" CssClass="modalPopupButton" runat="server" Text="Do Nothing" />
                    </div>
                    <br />
                </asp:Panel>
               <asp:DropDownList ID="DropDownList_sequences" runat="server" AutoPostBack="True"
                    DataSourceID="ds1" DataTextField="actionSequenceName" DataValueField="actionSequenceKey"
                    OnSelectedIndexChanged="Page_Load" CssClass="dropDownList">
                </asp:DropDownList>
                <asp:SqlDataSource ID="ds1" runat="server" ConnectionString="<%$ cs1 %>"
                    SelectCommand="xxxxx"></asp:SqlDataSource>
                <br />
                <br />
                <asp:GridView ID="GridView_actionOrder" runat="server" AutoGenerateColumns="False"
                    DataSourceID="xxxxxx" DataKeyNames="Id" Width="300px" CssClass="gridView"
                    AllowPaging="True" AllowSorting="True">
					   <HeaderStyle CssClass="headerStyle" />
                    <Columns>
                        <asp:TemplateField HeaderText="xxxxx">
                            <ItemTemplate>
                                <asp:Panel ID="PopupMenu" runat="server" CssClass="popupMenu">
                                    <asp:ImageButton ID="Image_actionUP" runat="server" src="Images/blue_up.gif" CommandName="up"
                                        CommandArgument='xxx'
                                        OnCommand="sequenceJobsGrid_onClick" Height="15px" Width="15px" />&nbsp;<asp:ImageButton
                                            ID="Image_actionDOWN" runat="server" src="Images/green_down.gif" CommandName="down"
                                            CommandArgument='xxxx'
                                            OnCommand="sequenceJobsGrid_onClick" Height="15px" Width="15px" /><br />
                                    <asp:ImageButton ID="Image_actionDELETE" runat="server" src="Images/red_delete.gif"
                                        CommandName="remove" CommandArgument='xxxx'
                                        OnCommand="sequenceJobsGrid_onClick" Height="15px" Width="15px" />
                                    <cc1:ConfirmButtonExtender ID="cbe_deleteStep" runat="server" TargetControlID="Image_actionDELETE"
                                        DisplayModalPopupID="modal_delete" />
                                    <asp:ImageButton ID="Image_actionPLUS" runat="server" src="Images/green_plus.png"
                                        CommandName="add" CommandArgument='xxxx'
                                        OnCommand="sequenceJobsGrid_onClick" Height="15px" Width="15px" />
                                    <br />
                                </asp:Panel>
                                <cc1:ModalPopupExtender runat="server" ID="modal_delete" TargetControlID="Image_actionDELETE"
                                    PopupControlID="panel_deleteStep" DropShadow="true" OkControlID="OkButton" CancelControlID="CancelButton"
                                    BackgroundCssClass="modalBackground" RepositionMode="RepositionOnWindowResizeAndScroll" />
                                <asp:Panel ID="panel_deleteStep" runat="server" CssClass="modalPopup" Width="300px"
                                    EnableTheming="False" EnableViewState="False">
                                    xxxxxxxx
                                    <br />
                                    <font color="#FF0000"><b>xxxxxx</b></font><br />
                                    xxxxxx
                                    <br />
                                    <br />
                                    <div align="center">
                                        <asp:Button ID="OkButton" CssClass="modalPopupButton" runat="server" Text="Remove Step" />
                                        <asp:Button ID="CancelButton" CssClass="modalPopupButton" runat="server" Text="Do Nothing" />
                                    </div>
                                </asp:Panel>
                                <asp:Panel runat="server" ID="d1">
                                    <asp:Label ID="l1" runat="server" Text='xxxx'></asp:Label>
                                </asp:Panel>
                                <cc1:HoverMenuExtender ID="HoverMenuExtender1" runat="server" PopupControlID="PopupMenu"
                                    TargetControlID="d1" PopupPosition="Right" OffsetX="0" HoverCssClass="popupHover">
                                </cc1:HoverMenuExtender>
                                <cc1:ModalPopupExtender runat="server" ID="ModalPopupExtender1" TargetControlID="Image_actionPlus"
                                    PopupControlID="panel_addStep" DropShadow="false" OkControlID="OkButton" CancelControlID="CancelButton"
                                    BackgroundCssClass="modalBackground" />
                                <asp:Panel ID="panel_addStep" runat="server" CssClass="modalPopup" Width="400px">
                                    What step would you like to add to the sequence?
                                    <br />
                                    <br />
                                    <asp:DropDownList ID="DropDownList_jobsToAdd" runat="server" DataSourceID="xxxxxx"
                                        DataTextField="name" DataValueField="name" CssClass="dropDownList">
                                    </asp:DropDownList>
                                    <br />
                                    <br />
                                    <div align="center">
                                        <asp:Button ID="Button1" CssClass="modalPopupButton" runat="server" Text="Add Step" />
                                        <asp:Button ID="Button2" CssClass="modalPopupButton" runat="server" Text="Do Nothing" />
                                    </div>
                                </asp:Panel>
                            </ItemTemplate>
                        </asp:TemplateField>
                    </Columns>
				</asp:GridView>
                <asp:SqlDataSource ID="xxxxxx" runat="server" ConnectionString="<%$ cs1 %>"
                    SelectCommand=".....">
                    <SelectParameters>
                        <asp:Parameter DefaultValue="...." Name="....." Type="String" />
                        <asp:ControlParameter ControlID="DropDownList_sequences" DefaultValue="1" Name="actionSequenceKey"
                            PropertyName="SelectedValue" Type="String" />
                        <asp:Parameter Name="query" Type="String" DefaultValue=" " />
                    </SelectParameters>
                </asp:SqlDataSource>
            </ContentTemplate>
            <Triggers>
                <asp:AsyncPostBackTrigger ControlID="DropDownList_sequences" EventName="SelectedIndexChanged" />
            </Triggers>
        </asp:UpdatePanel>
    </div>
 
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CodeBehind File
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public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
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.            
    }
 
    void LinkButton_cloneSequence_Click(object sender, EventArgs e)
    {
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.
    }
 
    void DropDownList_sequences_PreRender(object sender, EventArgs e)
    {
.
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.
.
    }
 
    protected void sequenceJobsGrid_onClick(object sender, CommandEventArgs e)
    {
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}

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