I was trying to update Oxwall and after entering the FTP details and clicking OK, it took me to a blank white page. No update was done and the website is now showing e500 and '404 Not Found'. I've tried to fix it with the sticky post about changing the public function checkUpdate()? That didn't fix it.

The website is www.meetplace.net

Looking in the error_log file, this is what it says:
PHP Fatal error: Call to undefined method OW_SystemPlugin::getApiCtrlDir() in /home1/meetplac/public_html/www/ow_core/plugin_manager.php on line 136

How do I fix it?