Hey there,
We ran into an issue with the packaging of the 4.3.1 update of The Events Calendar, Event Tickets, and Events Calendar Pro.
The main way to resolve these problems is to DELETE previously-installed versions of these three plugins. This will not delete event or tickets data.
Once done, then download fresh copies of plugin files. You can do so for The Events Calendar 4.3.1.1 at http://wordpress.org/plugins/the-events-calendar
Ensure that you install fresh new copies of The Events Calendar 4.3.1.1, not 4.3.1. Same for Events Calendar Pro if you have it: install fresh copies for 4.3.1.1, which we released Thursday evening, and Event Tickets 4.3.1.1
Thank you so much for your patience! Please let us know if you have further questions on this matter or anything else we can try to help with.
Sincerely,
George