ModalPopupExtender showing error for linkbutton in reapeter

<script language="javascript" type="text/javascript">

        function ShowEditModal(Eid) {

            var frame = $get('IframeEdit');

            frame.src = "View_Batch.aspx?ID=" + Eid;

            //frame.scrolling=true;

            frame.height = 800;

            frame.width = 550;

            $find('EditModalPopup').show();

        }

    script>

<asp:UpdatePanel ID="updpnlBatch" runat="server">

                        <ContentTemplate>

                            <asp:Repeater ID="rptBatch" runat="server" EnableViewState="True" OnItemCommand="rptBatch_ItemCommand"

                                OnItemDataBound="rptBatch_ItemDataBound">

                                <HeaderTemplate>

                                    <table border="0" cellpadding="4" cellspacing="1" width="98%">

                                            <td align="left" bgcolor="#C1C5B8" class="white" width="16%">

                                                <b>Editb>

                                            td>

                                        tr>

                                    table>

                                HeaderTemplate>

                                <ItemTemplate>

                                    <table border="0" cellpadding="4" cellspacing="1" width="98%">

                                        <tr>

                                            <td align="left" class="hometext10" width="16%" bgcolor="#f5f5f5">

                                                <asp:LinkButton ID="lnkbtnBatch" runat="server" CssClass="orange">View/ Editasp:LinkButton>

                                            td>

                                        tr>

                                    table>

                                ItemTemplate>

                            asp:Repeater>

                        ContentTemplate>

                    asp:UpdatePanel>

<asp:Button ID="btnBatchEditt" runat="server" Text="Referee Report" Style="display: none" />

        <cc1:ModalPopupExtender ID="mpexBatch" runat="server" BackgroundCssClass="modalBackground"

            CancelControlID="btnBatchEditCancel" OkControlID="btnBatchEditDone" TargetControlID="btnBatchEditt"

            PopupControlID="DivEditWindow" BehaviorID="EditModalPopup">

        cc1:ModalPopupExtender>

        <div class="popup_Buttons" style="display: none">

            <input id="btnBatchEditDone" value="Done" type="button" />

            <input id="btnBatchEditCancel" value="Cancel" type="button" />

        div>

        <div id="DivEditWindow" style="display: none;">

            <iframe id="IframeEdit" frameborder="0" width="400">iframe>

        div>

ON .CS :

protected void rptBatch_ItemDataBound(object sender, RepeaterItemEventArgs e)

    {

if (e.Item.ItemType == ListItemType.Item || e.Item.ItemType == ListItemType.AlternatingItem)

            {

                LinkButton LbtnBatch = (LinkButton)e.Item.FindControl("lnkbtnBatch");

                LbtnBatch.Attributes.Add("onClick", "ShowEditModal('" + id + "');");

        }

}

 the modelpopup close with in seconds