Good evening Allison and welcome to the Events Calendar Support forum!
Thank you for reaching out to us.
We are sorry to hear about the Fatal error message.
I would love to help you with this topic.
What’s going on is that you are using a template customization ( you might want to read our Themer’s guide to get a sense of how that works) that needs updating to work properly with the latest version of our plugin.
I would recommend reading my colleague Brian’s post on this: https://theeventscalendar.com/support/forums/topic/fatal-error-code-on-event-pages-i-have-up-to-date-version-of-events-cal-pro/
With that, you should find the code that needs replacement in wp-content/your-theme-name/tribe-events/
But let me know if you require help for that part
Have a good week-end,
Geoff B.