Link to patch fix file: https://www.dropbox.com/s/wola0zd03x51wwr/class-admin-ajax.php?dl=0
Replace location: …/eventon/includes/admin
How to replace
First download the patch fix file from above link. And then connect to your website’s files via a FTP client, or using file manage in cpanel. (If you are unsure of these, please consult your website host) and location the above mentioned folder on eventon plugin. Replace the downloaded patch file in that folder. Go into your website wp-admin and clear cache on your website (if using cache services) and refresh browser.