I'm blogging this because I get this error occationally when I restart Tomcat with ACF8 deployed as a WAR:
The Cron service is not available.
This happens because the neo-cron.xml file in /WEB-INF/cfusion/lib has been corrupted. You can replace it with the neo-cron.bk file however in my case that file is always corrupted as well.
Here is a basic cron file if you have an empty backup file as well: