[User Error] Uncaught ReflectionException: Class {Classname} does not exist

<%- if @topic_view.topic.tags.present? %>
<%= t 'js.tagging.tags' %>: <%- @topic_view.topic.tags.each do |t| %> <%= t %> <%- end %>
<% end %>

Silverstripe Version: 3.7.3

I’m having issues with a instance of Silverstripe on a PLESK server, I believe it is a configuration issue as a few pages work, however some classes are throwing exceptions as shown below.

The same code works on a dev server, and I’ve had to work on a few items to allow the site to work as it does currently, open_base_dir, is there an obvious configuration option missing to ensure the classes work, they do exist, and run 100% on a dev server. I’ve checked all the PHP modules and everything appears to be as it should from that perspective. Is there a location
/dev/build?flush=1 runs successfully and displays the classes shown in the exception.

[User Error] Uncaught ReflectionException: Class {Classname} does not exist

5 /**
6  * A class for creating new objects by the injector.
7  *
8  * @package framework
9  * @subpackage injector
10  */
11 class InjectionCreator implements Factory {
12 
13 	public function create($class, array $params = array()) {
14 		$reflector = new ReflectionClass($class);
15 
16 		if (count($params)) {
17 			return $reflector->newInstanceArgs($params);
18 		}
19 
20 		return $reflector->newInstance();