updatePanel and Response.xxx

I have the following C# code. Once the "open" button was clicked, this code will open a pdf file.

1    Response.ContentType = "text/pdf";
2    Response.AppendHeader("Content-Disposition", "attachment; filename=report.pdf");
3    Response.TransmitFile("reports/" + this.Master.Username.Text.Trim() + ".pdf");
4    Response.End();

It works fine by itself, but I need to the button into an updatePanel. Once the button is in a updatePanel, it won't work and will give me error complaining about response.write...etc.Anybody get any ideas?
 

 
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