Ajax:ModalPopup js exception, BackgroundCssClass is null

Question

I use a modal popup extender, i followed all the instructions on the toolkit sample page, except that i didn't set the property BackgroundCssClass.

this is what happens:

Is there a way I can get rude of it without setting the cssclass prop? I don't need any styles.

If the answer is NO then please show me an example how to set it with a cssclass (even dummy).

Thanks in advance.

Here is the code:

<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<div>
    <div style="size: 100%; vertical-align: middle">
        <asp:LinkButton ID="lnkUpload" Text="Upload" ToolTip="Upload new file" runat="server" OnClick="lnkUpload_Click" />
        <cc1:ModalPopupExtender ID="lnkUpload_ModalPopupExtender" runat="server" Drag="true" PopupDragHandleControlID="pnlUploadTitle" DynamicServicePath="" PopupControlID="pnlUpload" Enabled="True" TargetControlID="lnkUpload" CancelControlID="btnCancel" />
    </div>
    <asp:Panel ID="pnlUploadTitle" runat="server" Visible="false">
        <center>
            Upload file
        </center>
    </asp:Panel>
    <asp:Panel ID="pnlUpload" runat="server" Visible="false">
        <center>
            <br />
            <asp:FileUpload ID="upFiles" runat="server" /><br />
            <br />
            <asp:Button ID="btnUpload" runat="server" Text="Upload" OnClick="btnUpload_Click" />
            &nbsp;<asp:Button ID="btnCancel" runat="server" Text="Cancel" />
            <br />
        </center>
    </asp:Panel>
</div>
</form>

Answer 1

You can set the ModalPopupExtender's backgroundCssClass within the actual HTML markup.

Example from the asp.net modal popup page:

<ajaxToolkit:ModalPopupExtender ID="MPE" runat="server"
TargetControlID="LinkButton1"
PopupControlID="Panel1"
**BackgroundCssClass="modalBackground"** 
DropShadow="true" 
OkControlID="OkButton" 
OnOkScript="onOk()"
CancelControlID="CancelButton" 
PopupDragHandleControlID="Panel3" />