Any Campaign Creators Know What's Happening?

Hey guys, I just tried publishing a private testing version of my own campaign and had my friend install it - the install went fine and he didn't have any errors pop up until he tried pressing play . This is what it said:

https://preview.redd.it/7m66ar0orc5e1.png?width=1366&format=png&auto=webp&s=38966cbb969ab547cba9eb16922f54a14a0cefef

Anyone know what issues may be causing this? I've configured a missions.txt file and everything and I uploaded the entire campaign up to the workshop and this issue doesn't seem to have any possible causes, at least to myself.