Hi,
Sorry for the SPAM issues. I can give some pointers on registration, but first.
When I visit your Submit Form:
yoursite.com/events/community/add
I do not see the reCAPTCHA activated.
Can you confirm it is active here:
Events > Settings > Community Tab > “reCAPTCHA API Keys”
If you have the keys in maybe try new ones and if that still does not work do you have any customizations that might have added reCAPTCHA before we added it as a feature?
Or any custom Community Event Templates in your theme?
Let me know what you find out.
Thanks