Why I am I am getting error msg as "Internet Explorer cannot download x.aspx from the https site in web server?

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C#2.0

C#

ASP.NET

IIS7.5

I am having few files of format (pdf,.xls,.doc etc) but on downloading from web server I am getting error msg as Internet Explorer cannot download x.aspx from the site. Internet explorer cannot open the site. The requested site is either unavailable or try again later.Its an https site.In local its fine and all basic softwares are there in server too. All are set with in the tables (template name-x.xls/x.pdf etc are in the table)
Code as follows:

String strFile = String.Empty;
           String[] filename;

           strFile = Server.MapPath(ConfigurationManager.AppSettings["TemplatePath"].ToString()) + FileName;

           filename = strFile.Split('\\');

           Response.Clear();
           Response.Buffer = true;// Read the original file from diskFileStream *
           Response.AddHeader("Content-Disposition", "attachment; filename=" + filename[filename.Length-1]);


           String ext = String.Empty;
           if (strFile.IndexOf(".") > 0)
               ext = (strFile.Split('.'))[1];

           if (ext.ToLower() == "txt")
               Response.ContentType = "text/html";
           if (ext.ToLower() == "xls")
               Response.ContentType = "xls/html";
           if (ext.ToLower() == "pdf")
               Response.ContentType = "application/pdf";

           ////combine the path and file name
           if (File.Exists(strFile))//open the file and process it
           {
               FileStream sourceFile = new FileStream(strFile, FileMode.Open, FileAccess.Read);
               long FileSize;
               FileSize = sourceFile.Length;
               Response.AddHeader("Content-Length", FileSize.ToString()); //*
               byte[] getContent = new byte[(int)FileSize];
               sourceFile.Read(getContent, 0, (int)FileSize);

               sourceFile.Close();
               Response.BinaryWrite(getContent);
           }