I refreshed all events and the problem went away. What happens now is that after registering, I keep getting the error :
"You must provide at least one recipient email address." -- I also get this from backend sometimes
Then I get the message
"Your booking was successfull! The administrator has booked the following event for you."
This is good, but it seems ugly when it appears at the top of the page.
You can try registering for an event and see it for yourself at
learn.afrinic.net/index.php/events/events-schedule
Thanks for your help