为什么在服务器端生成Excel文件后再下载时，总是出现白屏？50分！

执行CmdDownload_Click事件时，如果生成的Excel行数超过10行左右时，
就会出现白屏，如何解决？    Private Sub CmdDownload_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn_Print.Click
        Dim CPrint As New BLL.Quote.CQuotePrint, RefFileName As String = ""
        Dim sSaveAsPath As String = ConfigurationSettings.AppSettings("BillSaveAsPath")
        Dim RefMsg As String = ""
        CPrint.CN = CType(Session(BLL.UserInfoConstant.SESSION_USER_CON_CN), ADODB.Connection)
        RefMsg = CPrint.Print(txt_Quotenum.Text.Trim, RefFileName, Session(BLL.UserInfoConstant.SESSION_USER_INFO_DEFAULT_OWNTEL))
        Dim CCommon As New Common.CommonClass
        If RefMsg <> "" Then
            CCommon.MsgBox(RefMsg, Me)
            Exit Sub
        Else
            Response.Write("<script language=javascript>window.open('../DownLoad.aspx?frmFold=" + sSaveAsPath + "&frmQuote_file=" + RefFileName + "','DownLoad','height=100,width=400,top=100,left=100,toolbar=no,menubar=no,scrollbars=no, resizable=no,location=no, status=no');</script>")
        End If
    End Sub
    
'''''''''''''''''''''''''''''''''''''''''''
'Download.aspx
'''''''''''''''''''''''''''''''''''''''''''   Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        '&Ocirc;&Uacute;&acute;&Euml;&acute;&brvbar;·&Aring;&Ouml;&Atilde;&sup3;&otilde;&Ecirc;&frac14;&raquo;&macr;&Ograve;&sup3;&micro;&Auml;&Oacute;&Atilde;&raquo;§&acute;ú&Acirc;&euml;
        If Me.IsPostBack = False Then
            DownLoadBill(Request("frmFold"), Request("frmQuote_file"))
        End If
    End Sub    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