请问怎么执行这两句代码时，出现白屏（界面白色）？应该怎么改？

Question

Private Sub DownLoadBill(ByVal PathName As String, ByVal FileName As String)
        Dim name As String
        Dim aFile As System.IO.FileInfo
        Dim na As String
        name = PathName + FileName
        aFile = New System.IO.FileInfo(Server.MapPath(name))
        na = System.IO.Path.GetFileName(name)
        Response.Clear()
        Response.ClearHeaders()
        Response.BufferOutput = False
        Response.ContentType = "application/octet-stream"
        Response.AppendHeader("Content-disposition", "attachment;filename=" + HttpUtility.UrlEncode(FileName, System.Text.Encoding.UTF8))
        Response.AddHeader("Content-Length", aFile.Length.ToString())
        Response.WriteFile(name)
        Response.Flush()
        Response.End()
    End Sub