Hi,
Sorry for the issues you are having. I can help out here.
I am not able to reproduce the issue on my site, but it looks to be a bad update for Event Tickets Plus.
You are going to have to go in by ftp or through your hosting’s file manager and remove Event Tickets Plus from the plugin directory.
wp-content/plugins/event-tickets-plus
Then you will want to update The Events Calendar and Event Tickets to 4.2
And finally get the latest version of Event Tickets Plus (4.2) from your account here on theeventscalendar.com
After that you should be able to activate everything without issue.
This entire process does not delete or change settings or events so you should not lose any data.
Let me know how that works out.
Thanks