Looking at my logs this morning I got this:

2005-04-18 07:23:40,296 ERROR [confluence.importexport.impl.BackupJob] Error while running the scheduled 'Backup'!
java.lang.NullPointerException
at bucket.util.FileUtils.copyFile(FileUtils.java:69)
at bucket.util.FileUtils.copyFile(FileUtils.java:63)
at com.atlassian.confluence.importexport.impl.BackupJob.execute(BackupJob.java:65)
at org.quartz.core.JobRunShell.run(JobRunShell.java:191)
at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:516)

My backup directory is set to: C:\tmp\uat2\backups

That directory exists but is empty after this error.