So recently I’ve had to change the php mode from Fast CGI to Apache Module in plesk due to the http authenticate functions in php not working. This caused my Zend Framework website to produce a 500 error, in my case it was something to do with:

Fatal error: Uncaught exception 'Zend_Session_Exception' with message 'session has already been started by session.auto-start or session_start()

The reason for the error is that the session already existed from my first visit and CGI was the owner, when I changed it to Apache module apache did not have permission to change the session data. The solution, shut down your browser (or start a privacy mode) and then try and view your website. Everything should work fine afterwards.