I am currently working on migrating the old website to this new server.

Important - PHP 8

There is an issue with the script in PHP 8 which is causing the calendar to not display properly.
Here is a quick fix for existing versions (no need to update):

In ac-includes > common.inc.php and change line 16 (latest version) from this:

//error_reporting(E_ALL ^ E_NOTICE);

to this:

error_reporting(0);

This code turns off PHP error reporting just for the calendar script.