Swarm Agent - Failed to cache the executable


I can’t build light.
Here the log of the swarm agent

18:54:23: [Interface:TryOpenConnection] Local connection established
18:54:26: [Job] Accepted Job C0183CE7-4F8EDA92-956A0D92-6CD6D252
18:54:28: [Interface:CacheAllFiles] Failed to cache the executable: C:\Unreal Engine 4.11\Engine\Binaries\Win64\UnrealLightmass.exe
18:54:35: [Job] AddTask: Rejected, cannot add a task to a running job
18:54:35: [CloseConnection] Closing connection 1E883796 using handle 1E883796
18:54:35: [CloseConnection] Connection confirmed for disconnection 1E883796
18:54:35: [CloseConnection] Closing orphaned Job (C0183CE7-4F8EDA92-956A0D92-6CD6D252)
18:54:35: [CloseConnection] Connection disconnected 1E883796
18:54:35: [GetMessage] Safely returning to 1E883796 with no message
18:54:36: [MaintainConnections] Local connection has closed (1E883796)
18:54:36: [MaintainConnections] Removed connection 1E883796
18:54:36: [MaintainConnections] All connections have closed

I have exactly the same config of swarm agents of UE4.10 where the problem doesn’t occur.

My project is the same than 4.10, I have just made changes on 3 materials after my really fresh migration to preview 8.

Tell me if you need other logs.

Thanks for your help and advises.

Sorry for disturbing! Answer Here:
[Swarm won't start. Won't build lighting - C++ - Unreal Engine Forums][1]


Thanks @Metathesus , that did it. There is also documentation, here, about the source engine version of UE needing to have Lightmass compiled from Visual Studio, quite commonly. Gives a lot of other Lightmass troubleshooting tips, as well.