The targetcontrolid of 'mpepopupinformation' is not valid. A control with ID 'lnkname' could not be found

Hi I am getting the following error: The TargetControlID of 'mpePopUpInformation' is not valid. A control with ID 'lnkName' could not be found.

I have 2 .master pages, in site.master page i have written  <asp:ScriptManager ID="ScriptMgrPopUp" runat="server"></asp:ScriptManager> and in staff.master page i am just inheriting <%@ Master Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true" CodeFile="Staff.master.cs" Inherits="Administration_Staff" %>
I do not where i am getting wrong. Can anyone guide me please? Thank you in advance.

I have user control which has one grid view:

<div class="panel panel-default">
    <div class="panel-body">
        <asp:updatepanel runat="server" id="updUserGrid" updatemode="conditional">
            <ContentTemplate>
               <asp:GridView ID="dgvUsers" runat="server" AutoGenerateColumns="false" GridLines="None" CssClass="tablemargin table table-condensed" Width="100%" AllowSorting="True">
                 <Columns>
                   <asp:TemplateField HeaderStyle-HorizontalAlign="Left" SortExpression="Name" HeaderText="Name">
                     <ItemTemplate>
                      <asp:LinkButton ID="lnkName" CommandName="Name" CausesValidation="false" runat="server"></asp:LinkButton>
                        </ItemTemplate>
                         </asp:TemplateField>                        
                 </Columns>
                </asp:GridView>
    </div>
    </ContentTemplate>
       </asp:UpdatePanel>
</div>

In the same user control I have written this for modal popup.

<form id="form1" runat="server">
    <div>
        <ccll:ModalPopupExtender ID="mpePopUpInformation" runat="server" PopupControlID="PanelInfo" TargetControlID="lnkName" CancelControlID="btnCloseInfo"></ccll:ModalPopupExtender>
        <asp:Panel ID="PanelInfo" runat="server" CssClass="modalpopup">
            <div class="modal-header">
                <button type="button" class="close" data-dismiss="modal" id="btnCloseInfo">×</button>
                <h3>Information</h3>
            </div>
            <div class="modal-body">
                <fieldset>
                    Register Successfully Please Cek Email for Verification
                </fieldset>
            </div>
        </asp:Panel>
    </div>
</form>