Backup completing with errors

I am consistently getting a backup completed with errors entry in the log. The entry says four files could not be backed up. No other application is open during the backup.How do I find out which four files are the problem, and how do I correct that?

I am consistently getting a backup completed with errors entry in the log. The entry says four files could not be backed up. No other application is open during the backup.How do I find out which four files are the problem, and how do I correct that?