I've commented out a line in the crontab on a debian server, which I guess was there by default yet was causing me to get error emails every hour:

# m h dom mon dow user  command
17 *   * * *   root    cd / && run-parts --report /etc/cron.hourly

However, the error emails keep coming in as if it hasn't been commented out. The error emails:

Subject: Cron <root@(none)> root    cd / && run-parts --report /etc/cron.hourly (failed)
/bin/sh: root: not found

Any ideas?