This should not happen because registered events are independent of RoboHelp project.
Are you sure about this happening while closing and re-opening the project?
What happens if you open some other project after registering an event?
The dialog you show is only for registering a new event. In the Script Explorer Pod, click the calendar icon with a 1 on it. That will give you a list of all registered events. Is your event included in that list?
Yes, my event is listed in the All Registered Events list and runs as expected after I un-registered and re-registered the event. Thank you for the assistance.