Client.DownloadFile(satellite_address, satellite_dir + satellite_file_name);

private void timer5_Tick(object sender, EventArgs e)
         {
             
            string Next_File;
            bool file_compare;
            int i;
            bool bad_file;
               file_array_dl = Directory.GetFiles(satellite_dir, "satellite*.jpg");

               if (file_array_dl.Length == 0)
               {
                   label6.Text = "Directory is empty therefore Showing sample image";
                   pictureBox1.Load(@"d:\Weather_Michmoret.bmp");
                   realtime_write_to_Log("Last Downloaded file is :" + satellite_dir + satellite_file_name + @"\satellite.jpg");
               }
               else
               {
                   //i = file_array_dl.Length; // Need to change to last_file_image()
                   i = last_satellite_file();
                   last_file = satellite_dir + @"\satellite" + i.ToString("D3") + ".jpg";
                   File.Copy(last_file, bad_file_test_dir + testing_file);
                   bad_file = Bad_File_Testing(bad_file_test_dir + testing_file);
                   if (bad_file == true)
                   {
                       File.Delete(bad_file_test_dir + testing_file);
                       if (File.Exists(last_file))
                       {
                           file_compare = File_Utility.File_Comparison(satellite_dir + satellite_file_name, last_file);
                           if (file_compare == true)
                           {
                               return;
                           }
                           //i = 0;
                           //i = file_array_dl.Length + 1;  // Need to change to last_file_image()
                           i = last_satellite_file() + 1;
                           Next_File = satellite_dir  + @"\satellite" + i.ToString("D3") + ".jpg";
                           File.Copy(satellite_dir + satellite_file_name, Next_File);
                           realtime_write_to_Log("Last Downloaded file is :" + Next_File);
                           pictureBox2.Load(Next_File);
                       }
                       else
                       {
                           File.Delete(last_file);
                           File.Delete(bad_file_test_dir + testing_file);
                       }
                   }
               }

i = last_satellite_file();

private int last_satellite_file()
         {
             int max_image_files_number = 0;
             string files_names = Directory.GetFiles(satellite_dir, "satellite*.jpg");
             for (int i = 0; i < files_names.Length; i++)
             {
                 string current_name = files_names;
                 int start_index = current_name.LastIndexOf("satellite") + 9;   // we get the starting index of radar and then add the length of 'radar', which is 5 
                 int last_index = current_name.LastIndexOf('.');
                 string image_file_number = current_name.Substring(start_index, last_index - start_index);
                 int image_file_number_converted = Convert.ToInt32(image_file_number);
                 if (image_file_number_converted > max_image_files_number)
                 {
                     max_image_files_number = image_file_number_converted;
                 }
             }
             return max_image_files_number;
         }

Formatexception was unhandled.
Input string was not in a correct format.
Make sure your method arguments are in the right format.
When converting a string to DateTime, Parse the string to take the date before putting each variable into the DateTime Object.