404 page when try to register for an event

I’m excited to get Events Planner working, but I’m having trouble getting it to work correctly.
I’m using this page as the main event registration page with some test events:
http://www.baisabe.com/wp/happenings/event-registration-2/ but when I click on “register” it gets me to a 404 page instead of the registration page.

I think it has something to do with the permalink structure because the 404 page has the url:
http://www.baisabe.com/wp/happenings/event-registration-2/?epl_action=process_cart_action&cart_action=add&event_id=1062

note how the ? for GET data follows the slash.

I’m not sure how to fix that.
Thanks in advance!

http://wordpress.org/plugins/events-planner/