Warning message: Configuration file is not found and cannot be created

I've been making scheduled daily backups of my data files without incident. Recently I saw the above warning message in the event log for a backup made a week ago, it also shows a green check mark. Each of the backup days before and after that day has a green check mark and no warning message. Today the same message appears in the log even though it is before the time the backup is scheduled to start. Anyone have any ideas and what is the configuration file that wasn't found?