下载打开PDF报错，其它文件OK

IE8, 在 SSL站点上下载、打开pdf文件，报如下的异常，原因是因为IE8的bug引起的。
https://support.microsoft.com/en-us/kb/323308 http://stackoverflow.com/questions/3415370/ie-unable-to-download-from-unable-to-open-this-internet-site-the-request
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Unable to download AttachmentsList.aspx from 192.168.0.50.

Unable to open this Internet site. The requested site is either unavailable or cannot be found. Please try again later.

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Response.Clear();
Response.AddHeader("Content-Disposition", "attachment; filename=" + HttpUtility.UrlEncode(fileName).Replace("+", "%20")); //resolve the filename with empty space char
Response.ContentType = "application/octet-stream";
Response.OutputStream.Write(buffer, 0, fileSize);
Response.Flush();
Response.Close();