Fix Error Unreal Lightmass executable is outdated - Recompile UnrealLightmass project with Development configuration in Visual Studio

You’ll see this if you are building the engine from source.

You can fix this by:

1. Go to Visual Studio.
2. Select UnrealLightmass as startup project.
3. Change config to Development Win64.
4. Right click and Build UnrealLightmass.

Make sure you don’t have unity build disabled locally otherwise it won’t work. Possibly because the light map system doesn’t recognize non-unity build lightmass exe because it has NonUnity in its name. Fix of this could be a pull request to the engine source.