<asp:Panel ID="ImagePanel" runat="server" BorderColor="Transparent" BorderStyle="None">
                         <asp:Button runat="server" ID="MultiSelect" CssClass="ContestAddBtn" Text="Upload File(s)" />
                         <CuteWebUI:UploadAttachments runat="server" ID="Uploader1" TempDirectory ='temp'
                            InsertButtonID='MultiSelect'
                            ProgressCtrlID='Uploader1Progress'
                         ProgressTextID='Uploader1ProgressText'
                            CancelAllMsg = "">
                        <VALIDATEOPTION AllowedFileExtensions="jpeg,jpg,gif,png" MaxSizeKB="1024" />
                        <TableStyle CssClass="AjaxUploaderAttachmentsTable" />

            <cc1:CollapsiblePanelExtender ID="CollapsiblePanelExtender4" runat="server" TargetControlID="ImagePanel"

            </cc1:CollapsiblePanelExtender>

 

 MultiSelect select button always disabled.... if we remove the CollapsiblePanelExtender, its working...