c++ C++ can't understand namespace in header?

[billw]

Trying to merge some changes against this file:

https://github.com/EpicGames/UnrealEngine/blob/release/Engine/Source/Programs/UnrealLightmass/Private/Lighting/Collision.h

The entire Lightmass namespace block is [unknown].

Any ideas on the problem here? I assume it is intended that namespace blocks are understood as they are pretty critical for C++!