503 Error when Using Multiple Themes with Coursepress

Good evening,

I am wanting to use Upfront with Coursepress Pro.
However, until Upfront and Coursepress have been made compatible (I understand this is still a work in progress), I want to use Upfront for my home page, and the Coursepress theme for all other pages.

There is a plugin which exists called 'Multiple Themes' by jonradio, which I have tried to use, however it returns a 503 error. I have looked it up, and it appears as if it might be an issue with Coursepress.

Do you have any insight into this and how I can work toward a solution?

Many thanks,
Simon