I am getting an email notification on a daily basis. Previously I was able to reboot the server and get the message to stop. Any suggestions on how to ensure this will not fail in the future?

The full email notification is:

/etc/cron.daily/logrotate:

cat: /opt/zimbra/log/logswatch.pid: No such file or directory
kill: usage: kill [-s sigspec | -n signum | -sigspec] [pid | job]... or kill -l [sigspec]
error: error running postrotate script