AJAX :: Download A File From Gridview Link Button?

I'm usign the following funtion to download a file from griview link button.

This code works fine without the Update Panel in the form.

If i put grid inside the updatepanel, i can't download the file. shows System.WebForms Cannot parse file.

//protected void LnkDownload_Click(object sender, EventArgs e)
//{
// LinkButton Lnk = sender as LinkButton;
// string filepath = Server.MapPath(Lnk.CommandArgument.ToString());
// System.IO.FileInfo myfile = new System.IO.FileInfo(filepath);
// if (myfile.Exists)
// {
// Response.ClearContent();
// Response.AddHeader("Content-Disposition", "attachment; filename=" + myfile.Name);
// Response.AddHeader("Content-Length", myfile.Length.ToString());
// Response.ContentType = "application//octet-stream";
// Response.TransmitFile(myfile.FullName);
// Response.End();
// }
//}