Index: backup/util/helper/backup_cron_helper.class.php
===================================================================
--- backup/util/helper/backup_cron_helper.class.php	(revision 13854)
+++ backup/util/helper/backup_cron_helper.class.php	(revision )
@@ -125,7 +125,7 @@
 
                 // Skip backup of unavailable courses that have remained unmodified in a month
                 $skipped = false;
-                if (empty($course->visible) && ($now - $course->timemodified) > 31*24*60*60) {  //Hidden + unmodified last month
+                if (empty($course->visible) && !empty($backupcourse->laststarttime) && ($now - $course->timemodified) > 31*24*60*60) {  //Hidden + unmodified last month
                     $backupcourse->laststatus = backup_cron_automated_helper::BACKUP_STATUS_SKIPPED;
                     $DB->update_record('backup_courses', $backupcourse);
                     mtrace('Skipping unchanged course '.$course->fullname);