I would take a look at the table cron_schedule and ensure that cron.php is setup and executing properly within the crontab daemon itself in your environment.
- http://www.magentocommerce.com/wiki/1_-_installation_and_configuration/how_to_setup_a_cron_job
Also, I think the M2E module requires that the admin Add Secret Key option must be disabled to work as well.
