If you get a critical error when clicking on an event, check to see if you are loading a form twice.
The error can be caused by other things but if you have a registration form attached to the event, you should only load it once via ONE of the methods below.
If you have two methods, remove one of them, then Save for This and Future Events, and Clear your Cache. That should fix the error.
If you are still getting an error, contact [email protected] with the link of the event so we can troubleshoot.