Interestingly The error occurs (not being able to update or add event tickets) when I activate my cache plugin without updating the page.
the error message is:
load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,jquery-ui-core,jquery-ui-widget,jquery-ui-po…:4 POST http://www.gilbertwhiteshouse.org.uk/site/wp-admin/admin-ajax.php 500 (Internal Server Error)
send @ load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,jquery-ui-core,jquery-ui-widget,jquery-ui-po…:4ajax @ load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,jquery-ui-core,jquery-ui-widget,jquery-ui-po…:4n.(anonymous function) @ load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,jquery-ui-core,jquery-ui-widget,jquery-ui-po…:4(anonymous function) @ tickets.js?ver=4.2.4:362dispatch @ load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,jquery-ui-core,jquery-ui-widget,jquery-ui-po…:3r.handle @ load-scripts.php?c=0&load[]=jquery-core,jquery-migrate,jquery-ui-core,jquery-ui-widget,jquery-ui-po…:3
Just thought this might help…