Strange lightmass bug - ExitCode error

Hey there, so this has just happened to me after I set up a build to run over night - ive built the lighting for this particular scene plenty of times before and had no issues until now. I start building and everything kicks off as per usual and then it just stops, there is no , lighting build failed or error prompt it just stops and acts as if its built the scene, going into the log I get this;

09:47:17: [Interface:TryOpenConnection] Local connection established
09:47:17: [Job] Accepted Job B01E8CE3-4F8A92C3-B7DEDE92-4CBA8374
09:47:18: [Job] Launched Job UnrealLightmass_2017-06-16_10-25-49_1064896-64bit.exe
09:47:18: [Job] PID is 4048
09:47:18: [Job] GUID is “B01E8CE3-4F8A92C3-B7DEDE92-4CBA8374”
09:47:18: [Connect] Successfully opened a remote connection with D38
09:47:18: [Connect] Successfully opened a remote connection with D37
09:47:18: [Connect] Successfully opened a remote connection with D36
09:47:18: [EndJobSpecification] Started job on remote connection
09:47:18: [Connect] Successfully opened a remote connection with D35
09:47:18: [EndJobSpecification] Started job on remote connection
09:47:18: [EndJobSpecification] Started job on remote connection
09:47:18: [SendMessage] Added alias for remote connection: 20F89C6C is an alias for 20F89C68
09:47:18: [EndJobSpecification] Started job on remote connection
09:47:19: [SendMessage] Added alias for remote connection: 20F89C6D is an alias for 20F89C6A
09:47:19: [SendMessage] Added alias for remote connection: 20F89C6E is an alias for 20F89C69
09:47:19: [SendMessage] Added alias for remote connection: 20F89C6F is an alias for 20F89C6B
09:47:19: LogLightmass:Display: Lightmass Win64 started on: DAVROS. Command-line: B01E8CE34F8A92C3B7DEDE924CBA8374
09:47:19: Failed to determine engine directory: Defaulting to …/…/…/Engine/
09:47:19: Lightmass Win64 started on: DAVROS. Command-line: B01E8CE34F8A92C3B7DEDE924CBA8374
09:47:19: LogLightmass:Display: Processing scene GUID: B01E8CE34F8A92C3B7DEDE924CBA8374 with 22 threads
09:47:19: Processing scene GUID: B01E8CE34F8A92C3B7DEDE924CBA8374 with 22 threads
09:47:19: Building static lighting…
09:47:19: [OpenConnection] Registering TCP channel …
09:47:19: [OpenConnection] Connecting to agent …
09:47:19: [TryOpenConnection] Testing the Agent
09:47:19: [TryOpenConnection] Opening Connection to Agent
09:47:19: [TryOpenConnection] Local Process ID is 4048
09:47:19: [Job] Found a parent connection for PID 4048
09:47:19: [Job] 20F89C67 → 20F89C70
09:47:19: [Interface:TryOpenConnection] Local connection established
09:47:19: Windows GetLastError: The operation completed successfully. (0)
09:47:19: LogWindows:Warning: CreateProc failed (2) …/…/…/Engine/Binaries/Win64/CrashReportClient.exe “C:/Program Files/Epic Games/UE_4.16/Engine/Binaries/DotNET/Engine/Programs/UnrealLightmass/Saved/Crashes/_0000” -AppName=UE4-UnrealLightmass -CrashGUID=_0000 -DebugSymbols=…\Engine\Intermediate\Symbols
09:47:19: [Job] Job has failed! Job executable didn’t exit cleanly. Exit code: -1066598274

09:47:19: [MaintainConnections] Detected dropped local connection, cleaning up (20F89C70)
09:47:19: [CloseConnection] Closing connection 20F89C70 using handle 20F89C70
09:47:19: [CloseConnection] Connection confirmed for disconnection 20F89C70
09:47:19: [CloseConnection] Connection disconnected 20F89C70
09:47:19: [GetMessage] Safely returning to 20F89C70 with no message
09:47:20: [CloseConnection] Closing connection 20F89C67 using handle 20F89C67
09:47:20: [CloseConnection] Connection confirmed for disconnection 20F89C67
09:47:20: [CloseConnection] Closing orphaned Job (B01E8CE3-4F8A92C3-B7DEDE92-4CBA8374)
09:47:20: [MaintainConnections] Connection 20F89C67 is DISCONNECTING
09:47:20: [MaintainConnections] Local connection has closed (20F89C70)
09:47:20: [MaintainConnections] Removed connection 20F89C70
09:47:24: [CloseConnection] Closing connection 20F89C6A using handle 20F89C6A
09:47:24: [CloseConnection] Connection confirmed for disconnection 20F89C6A
09:47:24: [CloseConnection] Closing connection 20F89C69 using handle 20F89C69
09:47:24: [CloseConnection] Connection confirmed for disconnection 20F89C69
09:47:24: [CloseConnection] Closing connection 20F89C68 using handle 20F89C68
09:47:24: [CloseConnection] Connection confirmed for disconnection 20F89C68
09:47:24: [CloseConnection] Closing connection 20F89C6B using handle 20F89C6B
09:47:24: [CloseConnection] Connection confirmed for disconnection 20F89C6B
09:47:24: [CloseConnection] Closing bi-directional remote connection (20F89C6B)
09:47:24: [CloseConnection] Closing bi-directional remote connection (20F89C6A)
09:47:24: [CloseConnection] Closing bi-directional remote connection (20F89C69)
09:47:24: [CloseConnection] Closing bi-directional remote connection (20F89C68)
09:47:24: [CloseConnection] Connection disconnected 20F89C6B
09:47:24: [CloseConnection] Connection disconnected 20F89C68
09:47:24: [CloseConnection] Connection disconnected 20F89C69
09:47:24: [CloseConnection] Connection disconnected 20F89C6A
09:47:25: [MaintainConnections] Connection 20F89C67 is DISCONNECTING
09:47:25: [MaintainConnections] Remote connection has closed (20F89C6E)
09:47:25: [MaintainConnections] Remote connection has closed (20F89C6C)
09:47:25: [MaintainConnections] Remote connection has closed (20F89C6A)
09:47:25: [MaintainConnections] Remote connection has closed (20F89C69)
09:47:25: [MaintainConnections] Remote connection has closed (20F89C68)
09:47:25: [MaintainConnections] Remote connection has closed (20F89C6B)
09:47:25: [MaintainConnections] Remote connection has closed (20F89C6F)
09:47:25: [MaintainConnections] Remote connection has closed (20F89C6D)
09:47:25: [MaintainConnections] Removed alias for remote connection: 20F89C6E was an alias for 20F89C69
09:47:25: [MaintainConnections] Removed connection 20F89C69
09:47:25: [MaintainConnections] Removed alias for remote connection: 20F89C6C was an alias for 20F89C68
09:47:25: [MaintainConnections] Removed connection 20F89C68
09:47:25: [MaintainConnections] Removed alias for remote connection: 20F89C6D was an alias for 20F89C6A
09:47:25: [MaintainConnections] Removed connection 20F89C6A
09:47:25: [MaintainConnections] Removed alias for remote connection: 20F89C6F was an alias for 20F89C6B
09:47:25: [MaintainConnections] Removed connection 20F89C6B
09:47:25: [MaintainConnections] Connection 20F89C67 is DISCONNECTING
09:47:26: [MaintainConnections] Connection 20F89C67 is DISCONNECTING
09:47:26: [MaintainConnections] Connection 20F89C67 is DISCONNECTING
09:47:27: [MaintainConnections] Connection 20F89C67 is DISCONNECTING
09:47:27: [MaintainConnections] Connection 20F89C67 is DISCONNECTING
09:47:28: [MaintainConnections] Connection 20F89C67 is DISCONNECTING
09:47:28: [MaintainConnections] Connection 20F89C67 is DISCONNECTING
09:47:29: [CloseConnection] Connection disconnected 20F89C67
09:47:29: [GetMessage] Safely returning to 20F89C67 with no message
09:47:29: [MaintainConnections] Local connection has closed (20F89C67)
09:47:29: [MaintainConnections] Removed connection 20F89C67
09:47:29: [MaintainConnections] All connections have closed

Ill say again, ive had no issues building lighting for this scene, I did a medium light build about a week ago and that worked perfectly fine - is there anyone here who can help?