For those experiencing this issue, first check to see if your WordPress environment has any errors with cron jobs. You can check by installing the WP Crontrol plugin and then navigate to Tools -> Cron Events and you’ll see an error at the top of the page if you have any.
Once you fix those errors, the Post Expirator plugin should work.
I just tested it on my WordPress 4.4.2 environment just fine.
