% sudo /usr/sbin/logrotate /etc/logrotate.conf
error: syslog-ng:1 duplicate log entry for /var/log/crond.log
error: found error in /var/log/messages.log /var/log/auth.log /var/log/mail.log /var/log/kernel.log /var/log/errors.log /var/log/daemon.log /var/log/user.log /var/log/iptables.log /var/log/everything.log /var/log/syslog.log /var/log/acpid.log /var/log/crond.log /var/log/lpr.log /var/log/uucp.log /var/log/news.log /var/log/ppp.log /var/log/debug.log , skipping

I think this says that /var/log/crond.log is specified in both /etc/logrotate.d/fcron (from the fcron package) and /etc/logrotate.d/syslog-ng (from the syslog-ng package), and that the whole syslog-ng log rotation script is skipped.