Hi Alexander,
If you are downloading the files on a Windows machine it could be that you have "hide extension for known filenames enabled" and therefore you are not viewing the proper extension and it could be you saved it with the wrong extension. If i download the latest version now, my filenames are correct. Since you are doing a long print we can at least test the following without updating the printer yet:
- If you are running Windows, make sure you have "extensions turned on", see: http://kb.winzip.com/kb/entry/26/ or https://www.thewindowsclub.com/show-file-extensions-in-windows.
- Then re-download the files from here: https://ultimaker.com/en/resources/23129-updating-the-firmware, check that the filenames are correct.
Kind regards,
Raymond.