This is DNN 5.1.4.  I need to upload a file to my portal folder, rename it, and then work with the renamed file. It does not work as I expect. The file is not always uploaded, and moving the file to a new name never works.  The following is my logic :

public static string[] ArchiveUpload(
   PortalSettings portalSettings,
   HttpPostedFile sourceFile
   ) {
   string[] filePaths = new string[2];

   FolderInfo uploadFolderInfo = GetUploadFolder(portalSettings, DefaultFolderName);
   string sourceFileName = uploadFolderInfo.PhysicalPath + sourceFile.FileName;
   string archiveFileName = uploadFolderInfo.PhysicalPath + sourceFile.FileName + DateTime.Now.ToString(".yyyyMMddhhmmss");

   FileSystemUtils.UploadFile(
      uploadFolderInfo.PhysicalPath,
      sourceFile,
      false
      );
   FileSystemUtils.MoveFile(
      sourceFileName, archiveFileName,
      portalSettings
      );

   filePaths[0] = sourceFileName;
   filePaths[1] = archiveFileName;
   return filePaths;
}

It looks pretty straightforward to me. I don't need to register these files to DNN as database resources. Or do I? What am I doing wrong?