Why does Response.Redirect close my browser window instead of redirecting

if (mode == "print")
    {
        error_code.Text = "";
        //thumb.Src = file_loc + "source/" + "certificate_thumbnail.jpeg";
        link.HRef = "Certificates/" + u_name + ".pdf";
        link.Visible = true;
        Response.Redirect("http://xx.xxxxxxxxxxxxx.xx.gov/cert/Certificates/" + u_name + ".pdf");


    }

Response.Redirect("http://www.google.com");