UPDATE: This fix is included in Ohanah 3.1.0 and it shouldn't be used anymore. Please upgrade your version of Ohanah.
Joomla 3.5.1 contains a code that exposes the bug that is in Joomla for years. It's a trivial bug, however exposing it has catastrophic consequences - it breaks email sending capabilities in ALL extensions. This bug affects Ohanah in a way that an error is shown after the purchase of the tickets (before redirecting to the PayPal). If you haven't upgraded to Joomla 3.5.1, please don't do it. Just wait for the next Joomla version. If you already updated, please replace this file /libraries/koowa/components/com_emails/controller/email.php with the file that you can find on this link
This is only a temporary fix until Joomla sort things out. We will see how things will develop with this bug and we will sort it out in next Ohanah release.