We have a similar problem to richard with the All-In-One Event Calendar plugin for WordPress. We're trying to change the Buy Tickets to Register for events, and we found your post really helpful because you had the same issue.
However, we are having a hard time finding where in WordPress you were able to find the event-single.php file. We are WordPress noobs :)
How did you navigate to finding the event-single.php file? Is it in the Plugins Editor for All-in-One Event Calendar? If so, which php file is it in, because we have searched and searched here and there is no event-single.php file listed in the Plugins Editor in the WordPress back end.
If you'd like to see our website, visit http://www.interweave.org.
Thanks a million!