Select a greyed out Custom event

Select a greyed out Custom event

In the past I have added a custom event in OP manager. After a while there was no need for this monitoring anymore so I deleted this event in the events screen.
Time goes by and now I need to monitor this events again. I see the Event log in my screen but when I select it I get the message "Eventlog file already exists".
 
How can I get this eventlog monitored again?
 
I've added some screenshots

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