Cron not working

[Haines Brown <haines@histomat.net>]

This may be a FAQ, but it has me stumped. I try to do a weekly backup
with this, but nothing happens, and there is nothing in syslog: 

  # crontab -l
  0 4 * * 0 /home/haines/scripts/backup

I can run the script manually with # /home/haines/scripts/backup.

Cron daemon is running:

  $ ps -ef | grep cron | grep -v grep
  root      8972     1  0 12:37 ?        00:00:00 cron