Good evening David and welcome back!
Thank you for reaching out to us.
We are sorry to hear about the fatal error message you received upon updating.
This was certainly unintended on our end and we apologize for the inconveniences this might have caused.
I would love to help you with this topic.
The first thing I would recommend is updating our core plugin ( the Events Calendar ) and Event Tickets to version 4.2.2 (they are both still at 4.2.1.1 on your installation).
Let me know how that goes.
Best regards,
Geoff B.