Lightmass crashed: Assertion failed: NumMaterialElements > 0

I am getting this error when doing the lighting build on a very large landscape, no added foliage or other meshes yet, just the plain landscape with materials added to it. Not sure how to correct his.

Error === Lightmass crashed: ===
Assertion failed: NumMaterialElements > 0 [File:D:\BuildFarm\buildmachine_++depot+UE4-Releases+4.8\Engine\Source\Programs\UnrealLightmass\Private\Lighting\LightingMesh.cpp] [Line: 108]

KERNELBASE.dll {0x00007ffb2285ec58} + 0 bytes
UnrealLightmass-Core.dll {0x00007ffb0219edbf} + 0 bytes
UnrealLightmass-Core.dll {0x00007ffb02081738} + 0 bytes
UnrealLightmass-Core.dll {0x00007ffb02062778} + 0 bytes
UnrealLightmass.exe!Lightmass::FStaticLightingMesh::Import() {0x00007ff69a1b7983} + 0 bytes
UnrealLightmass.exe!Lightmass::FLandscapeStaticLightingMesh::Import() {0x00007ff69a1b4ca5} + 0 bytes
UnrealLightmass.exe!Lightmass::FLightmassImporter::ImportObjectArray > >() {0x00007ff69a14fc63} + 0 bytes
UnrealLightmass.exe!Lightmass::FScene::Import() {0x00007ff69a1b65ec} + 0 bytes
UnrealLightmass.exe!Lightmass::FLightmassImporter::ImportScene() {0x00007ff69a1b82d0} + 0 bytes
UnrealLightmass.exe!Lightmass::BuildStaticLighting() {0x00007ff69a18299f} + 0 bytes
UnrealLightmass.exe!Lightmass::LightmassMain() {0x00007ff69a1bf3b8} + 0 bytes
UnrealLightmass.exe!main() {0x00007ff69a1dd94f} + 0 bytes
UnrealLightmass.exe!__tmainCRTStartup() {0x00007ff69a23950b} + 0 bytes
KERNEL32.DLL {0x00007ffb24c23b52} + 0 bytes
ntdll.dll {0x00007ffb266ea6f4} + 0 bytes
ntdll.dll {0x00007ffb266ea6f4} + 0 bytes

[File:D:\BuildFarm\buildmachine_++depot+UE4-Releases+4.8\Engine\Source\Programs\UnrealLightmass\Private\Lighting\LightingMesh.cpp] [Line: 108]

Do you have a lightmass importance volume covering the whole landscape? Also i wouldnt suggest using static lighting for large open world environments as you are bound to have problems with lightmass eventually.

Hi thanks for the suggestions. No my lightmass importance volume was not covering it all, does it work with multiple large lightmass volumes or better to use one for the entire landscape?

Sorry about the late response. Regarding multiple lightmass volumes; if you need to have global illumination for the whole landscape then 1 lightmass importance volume is all you need. If you want to have GI only for certain parts of the landscape then you can use separate lightmass importance volumes for those areas to minimize the build time. But in the end dynamic lighting is the best for large outside environments, in my opinion.

Removing the static lighting from the build corrected the problem, thanks for the suggestion.