I have LMS 2.5. And I get the version 3.0 with an upgrade license.
Do I uninstall the 2.5 version ? or install it on the same directory ? and do I need the two license files (2.5 and the 3.0 upgrade? )
Without seeing the whole log, or the file system layout, I would say that the backup directory was specified incorrectly, or that it was truly empty. Also, I suppose something could have happened to the backup during the first failed installation which resulted in some corruption leading the subsequent installation to think the directory did not contain a valid backup.
Your idea of doing a clean installation at this point is a good one.