So I’ve been breaking my head to get around this problem.
Encountered the error while following the step by step procedure stated in the tutorial link below, couldn’t get past step #8 under ‘Creating a GameMode’ section. The error pops up every time I try to compile the code via both unreal editor or visual studio for that matter.
Tutorial link: A new, community-hosted Unreal Engine Wiki - Announcements - Epic Developer Community Forums
Double check that your AFPSGameMode is inheriting from AGameMode and not AGameModeBase.