Modal Popup Error - asp.net

Question

I have a DataList that has a link button and I want this link button envoke a modal popup. I've copied the mpe code from another application where it works in a gridview. The error is thrown as soon as page is openned and each time the link button is clicked. The error is thrown in the ScriptResource file: "Microsoft JScript runtime error: Sys.ArgumentNullException: Value cannot be null.
Parameter name: elements". I understand something has null value but not sure what. Page has over a thousand lines so I'll just paste the part I'm working on.
<ItemTemplate>
<tr class="AssetMngnt-trHeaderRow_bgColor">
<td valign="top">
<asp:Label ID="lblIdent" runat="server" Text='<%# Eval("Printer_Ident") %>' Visible="false"></asp:Label>
</td>
<td>
<asp:LinkButton ID="lbEdit" runat="server" CausesValidation="False" CommandName="Select" Text="Edit" />
</td>
<td valign="top" nowrap>
<asp:Label ID="lblName" Text='<%# Eval("Network_Name") %>' runat="server" />
</td>
<td valign="top">
<asp:LinkButton ID="lbPrinterModel"
runat="server" CausesValidation="False" CommandName="Select" CommandArgument="ShowAsset"
Text='<%# Eval("Printer_Mfg") + " " + (string)Eval("Printer_Model") %>' />
</td>
<td valign="top">
<asp:Label ID="lblLocation" Text='<%# Eval("Location") %>' runat="server" />
</td>
<td>
<asp:LinkButton ID="LinkButton1"
runat="server" CausesValidation="False" CommandName="Select" CommandArgument="IssueToners"
Text="Issue Toners" />
<asp:Button runat="server" ID="btnShowPopup" style="display:none" />
<ajaxToolkit:ModalPopupExtender runat="server" id="mpeIssueToners"
TargetControlID="btnShowPopup"
PopupControlID="pnlFvIssueTonersModal"
CancelControlID="UpdateCancelButton"
BackgroundCssClass="modalBackground" >
</ajaxToolkit:ModalPopupExtender>
</td>
</tr>
</ItemTemplate>
<asp:Panel runat="server" ID="pnlFvIssueTonersModal" Visible="true" style="display:none">
<asp:Panel runat="server" ID="pnlFvIssueToners" Visible="true">
<div id="AssetMngnt-FloatLeft_alt"">
<!-- ISSUE TONERS FORM VIEW ******************************************************************************** -->
<asp:FormView ID="fvIssueCartridges" runat="server" DataSourceID="ODSIssueCartridges"
OnItemUpdating="fvIssueCartridges_OnItemUpdating" OnItemUpdated="FormView1_Display_Update_Msg"
EnableViewState="False"
EmptyDataRowStyle-CssClass="AssetMngnt-panelRO" >
<EditItemTemplate>
</EditItemTemplate>
</asp:FormView>
<!-- END ISSUE TONERS FORM VIEW **************************************************************************** -->
</div>
</asp:Panel>
<ajaxToolKit:ModalPopupExtender ID="ModalPopupExtender1" BehaviorID="mdlPopup" runat="server"
TargetControlID="div" PopupControlID="div" CancelControlID="btnNo"
OnCancelScript="cancelClick();" BackgroundCssClass="modalBackground" />
<div id="div" runat="server" align="center" class="confirm" style="display:none">
<asp:Label Text="Form is empty - empty records are not allowed."
ForeColor="#000000" runat="server" ID="Label3" /><br />
<asp:Button ID="btnNo" runat="server" Text="Ok" Width="50px" />
</div>
</asp:Panel>
The ModalPopupExtender1 takes care of things inside the FormView.
Thanks,
Risho