Admin Gantry page goes blank when I click on Layout / Settings etc

Hi, excuse my ignorance, I’m completely new to both Grav and Gantry and have just started playing around with it.

I’m getting a bank grey area in the content section of the admin panel when I select any of the link in the Gantry section: Layout / Page Setttings / Particle Defaults etc. The default Styles section works fine.

I must be missing something… What am I doing wrong? Should have installed / enabled something else?

Thanks for your help!