Plugin triggered fatal error

Noticed this plugin was inactive. When I tried to activate it I received a fatal error message below;

Plugin could not be activated because it triggered a fatal error.

Fatal error: Cannot redeclare _eventorganiser_set_constants() (previously declared in /home2/leisureg/public_html/inside/wp-content/plugins/event-organiser/event-organiser.php:49) in /home2/leisureg/public_html/inside/wp-content/plugins/event-organiser-org/event-organiser.php on line 58.

Can someone please help me with this.