The tinymce editor on my Event Page editor gets killed after activating Yoast WordPress SEO. The other tinymce editors on my site don't have this issue. I've been able to narrow it down to the Facebook Open Graph metadata option of YWP SEO. Activating it kills the tinymce editor, deactivating brings it back alive.
I've found a similar discussion (http://wordpress.org/support/topic/events-manager-and-wordpress-seo) dating over a year ago.
BTW Twitter causes the same problem, but that might be caused by the fact that I haven't validated Twitter Cards yet. Still need to test that. :)