Adding new post type fails

When I add a new post type the system displays the “Saving your changes” pop-up which stays there forever and never does anything!

The only thing I can see is that Debug Bar is showing a JavaScript error:

TypeError: undefined is not an object (evaluating ‘a.validator.methods[d].call’). Exception occurred when checking element slug, check the ‘nospecialchars’ method.
https://…/wp-content/plugins/tickera-event-ticketing-system/js/jquery.validate.min.js?ver=3.2.4.7 line 4

https://wordpress.org/plugins/types/