I backed up a course I made in my 2.8.1 test site (.mbz file). Tried to restore it in my live 2.8.1 site by dropping it in the upload box in Site admin > Courses > Course Restore.
Got this Debug message:
Error code: tmp_backup_directory_not_found
$a contents: [tempdir]/backup/6dc41d821874cef404a72c64640bd832
- line 140 of /backup/util/helper/convert_helper.class.php: convert_helper_exception thrown
- line 291 of /backup/util/helper/backup_general_helper.class.php: call to convert_helper::detect_moodle2_format()
- line 298 of /backup/util/ui/restore_ui_stage.class.php: call to backup_general_helper::detect_backup_format()
- line 123 of /backup/restore.php: call to restore_ui_stage_confirm->display()