In the source.aspx page, it has a asp.net UpdateProgress control and a button. The button onclick event redirect the response to generate the PDF using the RenderAsPDF method. The UpdateProgress showed up in the source aspx page while the printPDF.aspx is generating the pdf. Then, the File Download window appears to open or save the generated PDF. It works great but the MS UpdateProgress hang, i.e., does not disappear.

source.aspx.cs:
protected void cmdPrintPDF_Click(object sender, EventArgs e) {
Response.Redirect("http://website/printPDF.aspx");
}

printPDF.aspx has:
<eo:ASPXToPDF runat="server" ID="pdf"></eo:ASPXToPDF>

printPDF.aspx.cs has:
pdf.RenderAsPDF() as the last line in Page_Load()

It looks like the ajax call (button click) never ends (or retrun something back to the source.aspx) after redirect. The redirect actually is "downloading" a (dynamically-created) file (pdf).

How can I close the UpdateProgress control in source.aspx after redirect and file download from the printPDF.aspx?

You are correct. I was thinking about there might be some way to "terminate" it (in AfterRender). It turns out to be how the browser handle download file. Thanks.