Does not build lighting

hello

so, i’m under 4.8.2

my scene is pretty small, its a barn, fairly detailled, but not finished yet.
and, unreal wont buil the lighting anymore. it did earlier in the project, but then, it just stuck at 0% then disapear.
i imported the map in another project, same result. tried another computer, same result.

i’ve made my little homeworks and checked the internet for answers. someone brought up something with the swarm software. so i wen to see what the swarm had to say.

Building static lighting…
LogGenericPlatformMisc:Warning: Failed to determine engine directory: Defaulting to …/…/…/Engine/
Failed to determine engine directory: Defaulting to …/…/…/Engine/
[Job] Found a parent connection for PID 10124
[Job] 2035D015 → 3D2AC53E
[Interface:TryOpenConnection] Local connection established
LogUnrealMath:Error: FMatrix::InverseFast(), trying to invert a NIL matrix, this results in NaNs! Use Inverse() instead.
FMatrix::InverseFast(), trying to invert a NIL matrix, this results in NaNs! Use Inverse() instead.
=== Handled error: ===
Ensure condition failed: false [File:d:\buildfarm\buildmachine_++depot+ue4-releases+4.8\engine\source\runtime\core\public\math\UnrealMatrix.h] [Line: 266]
[Job] Job has failed! Job executable didn’t exit cleanly. Exit code: -1073741819
[CloseConnection] Closing connection 2035D015 using handle 2035D015
[CloseConnection] Connection confirmed for disconnection 2035D015
[CloseConnection] Closing orphaned Job

so to me it looks like a lot of fails
so, how do i fix this ?