Cron job fatal error - scheduled emails won't send. AddThis 5.0.7 issue
I have seen this error before with this plugin.   The CiviCRM cron job will fail if while bootstrapping WP a fatal error is encountered.  

My only workaround (besides removing the plugin as you did), is to launch the cron job via wp-cli.  See http://wiki.civicrm.org/confluence/display/CRMDOC/Managing+Scheduled+Jobs and the section on wp-cli.   In this case the flag --skip-plugins can be used to stop the addthis plugin from loading.