ModalPopupExtender conflict with download file via Response.BinaryWrite

Dear All:

I meet an big problem and can not fix it. While I use Response.BinaryWrite to download file directly, then 

the ModalPopupExtender become useless, that means when I click button , the UI not showing any thing about

ModalPopupExtender panel.

The Response.BinaryWrite code snippet is following:

ASP:<asp:UpdatePanel ID="uppnlDownloadFile" runat="server" UpdateMode="Always"><Triggers><asp:PostBackTrigger ControlID="btntest" /></Triggers>

C#:
string filename = "tt.xls";
Response.ContentType = "application/vnd.ms-excel";
Response.AddHeader("Content-Disposition", string.Format("attachment;filename={0}", filename));
Response.Clear();

using (HSSFWorkbook wb1 = new HSSFWorkbook())
{
	Response.BinaryWrite(WriteToStream(ReadDataTableToExcel(dt, sheetName, 1000)).GetBuffer());
}

Response.End();

And the use of modalpopupentendar is as following:

<asp:Button ID="btnDummy" runat="server" Style="visibility: hidden" /><cc3:ModalPopupExtender ID="ModalPopupExtenderCodeHandling" runat="server"
		BehaviorID="modalPopupExtenderCodeHandling"
		TargetControlID="btnDummy"
		PopupControlID="upnlCodeHandling"></cc3:ModalPopupExtender>

Is any way to solve that, thanks a lot.