no response when I click the ASP.NET button at the second time

There is an ASP.NET button which calls the following code.
Response.ClearHeaders();
Response.ClearContent();
Response.Clear();
Response.ContentEncoding = System.Text.Encoding.Default;
Response.AddHeader("content-disposition", "attachment; filename=excel.xls");
Response.ContentType = "application/ms-excel";
byte[] myExcel = System.IO.File.ReadAllBytes("excel.xls");
Response.OutputStream.Write(myExcel, 0, myExcel.Length);
Response.Flush();

When the button is first click, there is response and have excel download prompt, but there is no response when I click the button again.
why there is no response when I click the ASP.NET button at the second time? any resolution to it?