Why Internet Explorer not downloading files in https site with IE in IIS 7?

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VS2005

C#2.0

C#

IIS

Visual-Studio

Why Internet Explorer not downloading files in https site with IE browser in IIS 7? With http it works. We tried do not saving encrypted files to the disk in IE and also set cache header in web.config. Still the issue persists in IE. In all other browsers its fine.
My code as follows:

private void DownloadTemplate(string FileName)
 {
     try
     {

         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);
         }
         Common.UserPageAudit(Session["User"].ToString(), "Download Templates", Session["ROLE"].ToString(), strFile + " Template downloaded");
     }
     catch (Exception ex)
     {
         Response.Redirect("../CustomError.aspx?Err=" + ex.Message.ToString(), false);
     }
 }