Double prompt while File download in ASP.NET

[arc]

I am using this simple code snippet in downloading file but it gives me
double prompt while opening the file. Save is fine.
What could be the problem?

private void Page_Load(object sender, System.EventArgs e)

{

string sFilename = Request.QueryString["file"];

string sFile =
System.Configuration.ConfigurationSettings.AppSettings["FilePath"] +
sFilename;

Response.Clear();

Response.ContentType = "application/octet-stream";

Response.AddHeader("content-disposition", "attachment; filename=" +
sFilename.Substring(sFilename.IndexOf("_")+1));

Response.Flush();

Response.WriteFile(sFile);

}

Thanks
Arc