Media category permissions - error

[Mikethemix]

Affected version

MG 2.2.6 (running XF 2.2.16)

I am trying to set media category permissions to restrict access for a particular user or group.
However I get the following error message when attempting to view permissions of a media category:

An exception occurred: [InvalidArgumentException] Class XFMG\Permission\CategoryList does not match formatter pattern %s\%s\View\%s in src/XF.php on line 1129

1. XF::stringToClass() in src/XF/App.php at line 1667
2. XF\App->XF\{closure}() in src/XF/Container.php at line 234
3. XF\Container->create() in src/XF/Container.php at line 247
4. XF\Container->XF\{closure}() in src/XF/Mvc/Renderer/AbstractRenderer.php at line 80
5. XF\Mvc\Renderer\AbstractRenderer->createViewObject() in src/XF/Mvc/Renderer/AbstractRenderer.php at line 87
6. XF\Mvc\Renderer\AbstractRenderer->renderViewObject() in src/XF/Mvc/Renderer/Html.php at line 47
7. XF\Mvc\Renderer\Html->renderView() in src/XF/Mvc/Dispatcher.php at line 460
8. XF\Mvc\Dispatcher->renderView() in src/XF/Mvc/Dispatcher.php at line 442
9. XF\Mvc\Dispatcher->renderReply() in src/XF/Mvc/Dispatcher.php at line 402
10. XF\Mvc\Dispatcher->render() in src/XF/Mvc/Dispatcher.php at line 60
11. XF\Mvc\Dispatcher->run() in src/XF/App.php at line 2485
12. XF\App->run() in src/XF.php at line 524
13. XF::runApp() in admin.php at line 13

This error occurs irrespective of which Media Category I select
However if I select a Forum Node it works fine