Just another update to this conflict.
With updated versions on both plugins, we’re now getting these errors, if both plugins are turned on. With either plugin turned off, everything works fine.
[Mon Feb 02 15:42:36 2015] [error] [client 68.3.34.245] PHP Fatal error: Class ‘Tribe_Template_Factory’ not found in /nas/wp/www/cluster-1487/healthitanswer/wp-content/plugins/events-calendar-pro/lib/tribe-pro-template-factory.class.php on line 8, referer: http://www.healthitanswers.net/events/category/ourevents/list/
[Mon Feb 02 15:43:59 2015] [error] [client 68.180.228.173] PHP Fatal error: Class ‘Tribe_Template_Factory’ not found in /nas/wp/www/cluster-1487/healthitanswer/wp-content/plugins/events-calendar-pro/lib/tribe-pro-template-factory.class.php on line 8
[Mon Feb 02 15:53:59 2015] [error] [client 198.74.58.11] PHP Fatal error: Class ‘Tribe_Template_Factory’ not found in /nas/wp/www/cluster-1487/healthitanswer/wp-content/plugins/events-calendar-pro/lib/tribe-pro-template-factory.class.php on line 8
I have no clue why turning on Download Manager would cause this error in your plug-in.