As in title. 

Fresh install. No mods. Trying to play a Galaxy Forge map. Both players have the exact same map in the correct Galaxy Forge folder (we can both start it / host it / play it on single player). Get this error every time one of us tries to host and the other tries to join. What's more, we do NOT get this error if we both put the map into the "Map Designer" folder - but for some reason, all the maps in this folder end in and instant military defeat the moment they start. We can also connect and play the regular randomly generated maps (further confirming everyone is running same game client).

Spent two days trying to find a solution now, with all the previous posts made by other people pointing at the obvious (mods / wrong folder etc.) Would truly appreciate some help with this - I know it worked in the past as we played the exact same map a year or two ago, but I'm guessing some patch in between screwed something up.

Cheers and Happy New Year to everyone.