Can't save map after building light

After i build the light on my map (~10 hours) it looks good but for some reason when i try to save it, the following error shows up then the engine crashes without saving. Tried 2 times, same error every time. I dont know what it means.

Assertion failed: NewPosition >= 0 [File:X:\UnrealEngine\unreal Engine 4.4\Engine\Source\Runtime\Core\Private\Windows\WindowsPlatformFile.cpp] [Line: 62]

Stack:

FWindowsPlatformStackWalk::StackWalkAndDump() 0xd39e57e6 + 0 bytes [File=x:\unrealengine\unreal engine 4.4\engine\source\runtime\core\private\windows\windowsplatformstackwalk.cpp:177] [in F:\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-Core.dll]
FDebug::AssertFailed() 0xd3884525 + 0 bytes [File=x:\unrealengine\unreal engine 4.4\engine\source\runtime\core\private\misc\outputdevice.cpp:203] [in F:\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-Core.dll]
FFileHandleWindows::Seek() 0xd39d00e4 + 0 bytes [File=x:\unrealengine\unreal engine 4.4\engine\source\runtime\core\private\windows\windowsplatformfile.cpp:63] [in F:\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-Core.dll]
FArchiveFileWriterGeneric::Seek() 0xd37b50b4 + 15 bytes [File=x:\unrealengine\unreal engine 4.4\engine\source\runtime\core\private\hal\filemanagergeneric.cpp:696] [in F:\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-Core.dll]
FArchive::SerializeCompressed() 0xd394c7f9 + 0 bytes [File=x:\unrealengine\unreal engine 4.4\engine\source\runtime\core\private\serialization\archive.cpp:689] [in F:\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-Core.dll]
FUntypedBulkData::SerializeBulkData() 0xd6412f1c + 0 bytes [File=x:\unrealengine\unreal engine 4.4\engine\source\runtime\coreuobject\private\serialization\bulkdata.cpp:975] [in F:\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-CoreUObject.dll]
UPackage::SavePackage() 0xd64d72c7 + 0 bytes [File=x:\unrealengine\unreal engine 4.4\engine\source\runtime\coreuobject\private\uobject\savepackage.cpp:3390] [in F:\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-CoreUObject.dll]
UEditorEngine::SavePackage() 0xcbb6976b + 85 bytes [File=x:\unrealengine\unreal engine 4.4\engine\source\editor\unrealed\private\editor.cpp:4292] [in F:\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-UnrealEd.dll]
UEditorEngine::Exec_Obj() 0xcbc3faf5 + 68 bytes [File=x:\unrealengine\unreal engine 4.4\engine\source\editor\unrealed\private\editorserver.cpp:4036] [in F:\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-UnrealEd.dll]
UEditorEngine::Exec() 0xcbc3c9ac + 18 bytes [File=x:\unrealengine\unreal engine 4.4\engine\source\editor\unrealed\private\editorserver.cpp:5111] [in F:\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-UnrealEd.dll]
UUnrealEdEngine::Exec() 0xcbf5c8d0 + 17 bytes [File=x:\unrealengine\unreal engine 4.4\engine\source\editor\unrealed\private\unrealedsrv.cpp:704] [in F:\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-UnrealEd.dll]
SaveWorld() 0xcbcd66a9 + 135 bytes [File=x:\unrealengine\unreal engine 4.4\engine\source\editor\unrealed\private\filehelpers.cpp:508] [in F:\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-UnrealEd.dll]
FEditorFileUtils::SaveMap() 0xcbcd57d8 + 47 bytes [File=x:\unrealengine\unreal engine 4.4\engine\source\editor\unrealed\private\filehelpers.cpp:1837] [in F:\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-UnrealEd.dll]
SaveAsImplementation() 0xcbcd4c6d + 8 bytes [File=x:\unrealengine\unreal engine 4.4\engine\source\editor\unrealed\private\filehelpers.cpp:803] [in F:\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-UnrealEd.dll]
FEditorFileUtils::SaveAs() 0xcbcd3fba + 31 bytes [File=x:\unrealengine\unreal engine 4.4\engine\source\editor\unrealed\private\filehelpers.cpp:862] [in F:\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-UnrealEd.dll]
TBaseStaticDelegateInstance_NoParams::ExecuteIfSafe() 0xc768a71a + 0 bytes [File=x:\unrealengine\unreal engine 4.4\engine\source\runtime\core\public\delegates\delegateinstancesimpl.inl:690] [in F:\UnrealEngine-4.4.0-release\Engine\Binaries\Win64\UE4Editor-LevelEditor.dll]
FUICommandList::ExecuteAction() 0xd407cbb6 + 60 bytes [File=x:\unrealengine\unreal engine 4.4\engine\source\runtime\slate\private\framework\commands\u