Chances are, the latest version of the Galactic Civil War mod does not work with your version of Cosmoteer. This page has the previous versions of the GCW mod on it.
If by mistake you are here or wish to download the latest version of the GCW mod, please go to this page: https://forum.cosmoteer.net/d/5126-galactic-civil-war-2830-2837-battle-of-the-cosmos-0-3-0-14-1-compatible/112
This version is compatible with 0.13.X:
This version is compatible with 0.14.0:
This version is compatible with 0.14.1:
Sadly, there are no versions compatible earlier than 0.13.X