# === Lightmass crashed: ===

**URL:** <https://community.cesium.com/t/lightmass-crashed/24692>\
**Category:** Cesium for Unreal\
**Created:** [June 10, 2023, 8:42pm UTC](https://community.cesium.com/t/lightmass-crashed/24692 "2023-06-10T20:42:57Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![zhanglf1982](https://sea2.discourse-cdn.com/cesium/user_avatar/community.cesium.com/zhanglf1982/32/3476_2.png) [@zhanglf1982](https://community.cesium.com/u/zhanglf1982)\
**Post date:** [June 10, 2023, 8:42pm UTC](https://community.cesium.com/t/lightmass-crashed/24692/1 "2023-06-10T20:42:57Z")

</div>

=== Lightmass crashed: ===  
Assertion failed: (Index \>= 0) & (Index \< ArrayNum) [File:D:\build++UE5\Sync\Engine\Source\Runtime\Core\Public\Containers\Array.h] [Line: 691]  
Array index out of bounds: 1452 from an array of size 1452  
0x00007ff6be7f2dac UnrealLightmass.exe!Lightmass::FStaticMeshStaticLightingMesh::GetTriangleIndices()   
0x00007ff6be76b05a UnrealLightmass.exe!Lightmass::FEmbreeGeometry::FEmbreeGeometry()   
0x00007ff6be774f55 UnrealLightmass.exe!Lightmass::FEmbreeAggregateMesh::AddMesh()   
0x00007ff6be7c421e UnrealLightmass.exe!Lightmass::FStaticLightingSystem::FStaticLightingSystem()   
0x00007ff6be7798b1 UnrealLightmass.exe!Lightmass::BuildStaticLighting()   
0x00007ff6be79cda1 UnrealLightmass.exe!Lightmass::LightmassMain()   
0x00007ff6be7bcf97 UnrealLightmass.exe!main()   
0x00007ff6be825ebc UnrealLightmass.exe!\_\_scrt\_common\_main\_seh()   
0x00007fffcc6126ad KERNEL32.DLL!UnknownFunction   
0x00007fffcd86aa08 ntdll.dll!UnknownFunction   
\*\*\* CRITICAL ERROR! Machine: DESKTOP-SJBE0HN  
\*\*\* CRITICAL ERROR! Logfile: UnrealLight\_DESKTOP-SJBE0HN\_70633F284B00122BE7EFE3BD238A06F2.log  
\*\*\* CRITICAL ERROR! Crash report:  
LightingResults: Error: === Lightmass crashed: ===  
Assertion failed: (Index \>= 0) & (Index \< ArrayNum) [File:D:\build++UE5\Sync\Engine\Source\Runtime\Core\Public\Containers\Array.h] [Line: 691]  
Array index out of bounds: 1452 from an array of size 1452  
0x00007ff6be7f2dac UnrealLightmass.exe!Lightmass::FStaticMeshStaticLightingMesh::GetTriangleIndices()   
0x00007ff6be76b05a UnrealLightmass.exe!Lightmass::FEmbreeGeometry::FEmbreeGeometry()   
0x00007ff6be774f55 UnrealLightmass.exe!Lightmass::FEmbreeAggregateMesh::AddMesh()   
0x00007ff6be7c421e UnrealLightmass.exe!Lightmass::FStaticLightingSystem::FStaticLightingSystem()   
0x00007ff6be7798b1 UnrealLightmass.exe!Lightmass::BuildStaticLighting()   
0x00007ff6be79cda1 UnrealLightmass.exe!Lightmass::LightmassMain()   
0x00007ff6be7bcf97 UnrealLightmass.exe!main()   
0x00007ff6be825ebc UnrealLightmass.exe!\_\_scrt\_common\_main\_seh()   
0x00007fffcc6126ad KERNEL32.DLL!UnknownFunction   
0x00007fffcd86aa08 ntdll.dll!UnknownFunction   
Job has failed! Job executable didn’t exit cleanly. Exit code: 1  
LogStaticLightingSystem: Warning: Failed to build lighting!!! Lighting build failed.

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<div class="post-metadata">

**Author:** ![janine](https://sea2.discourse-cdn.com/cesium/user_avatar/community.cesium.com/janine/32/5135_2.png) [@janine](https://community.cesium.com/u/janine)\
**Post date:** [June 15, 2023, 1:15pm UTC](https://community.cesium.com/t/lightmass-crashed/24692/2 "2023-06-15T13:15:15Z")

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Does this happen in the Cesium for Unreal Samples project? If not, then it may be a separate problem with your own project that we won’t be able to diagnose.

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<div class="post-metadata">

**Author:** ![RuslanTRX](https://sea2.discourse-cdn.com/cesium/user_avatar/community.cesium.com/ruslantrx/32/14871_2.png) [@RuslanTRX](https://community.cesium.com/u/RuslanTRX)\
**Post date:** [July 18, 2023, 9:01am UTC](https://community.cesium.com/t/lightmass-crashed/24692/3 "2023-07-18T09:01:55Z")

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Same error happens to me.  
If you add a new project with VR template, create a new level and add cesium plugin - the same error will occur.

LightingResults: Error: === Lightmass crashed: ===  
Assertion failed: (Index \>= 0) & (Index \< ArrayNum) [File:D:\build++UE5\Sync\Engine\Source\Runtime\Core\Public\Containers\Array.h] [Line: 752]  
Array index out of bounds: 501 from an array of size 501  
0x00007ff6ecd09af3 UnrealLightmass.exe!Lightmass::FStaticMeshLOD::GetIndex()   
0x00007ff6ecd0af9d UnrealLightmass.exe!Lightmass::FStaticMeshStaticLightingMesh::GetTriangleIndices()   
0x00007ff6ecc7b3c9 UnrealLightmass.exe!Lightmass::FEmbreeGeometry::FEmbreeGeometry()   
0x00007ff6ecc8516a UnrealLightmass.exe!Lightmass::FEmbreeAggregateMesh::AddMesh()   
0x00007ff6eccda8f0 UnrealLightmass.exe!Lightmass::FStaticLightingSystem::FStaticLightingSystem()   
0x00007ff6ecc8bd71 UnrealLightmass.exe!Lightmass::BuildStaticLighting()   
0x00007ff6eccb10eb UnrealLightmass.exe!Lightmass::LightmassMain()   
0x00007ff6eccd3410 UnrealLightmass.exe!main()   
0x00007ff6ecd416cc UnrealLightmass.exe!\_\_scrt\_common\_main\_seh()   
0x00007ff8840626ad KERNEL32.DLL!UnknownFunction   
0x00007ff884daaa68 ntdll.dll!UnknownFunction   
0x00007ff6ecd09af3 UnrealLightmass.exe!Lightmass::FStaticMeshLOD::GetIndex()   
0x00007ff6ecd0af9d UnrealLightmass.exe!Lightmass::FStaticMeshStaticLightingMesh::GetTriangleIndices()   
0x00007ff6ecc7b3c9 UnrealLightmass.exe!Lightmass::FEmbreeGeometry::FEmbreeGeometry()   
0x00007ff6ecc8516a UnrealLightmass.exe!Lightmass::FEmbreeAggregateMesh::AddMesh()   
0x00007ff6eccda8f0 UnrealLightmass.exe!Lightmass::FStaticLightingSystem::FStaticLightingSystem()   
0x00007ff6ecc8bd71 UnrealLightmass.exe!Lightmass::BuildStaticLighting()   
0x00007ff6eccb10eb UnrealLightmass.exe!Lightmass::LightmassMain()   
0x00007ff6eccd3410 UnrealLightmass.exe!main()   
0x00007ff6ecd416cc UnrealLightmass.exe!\_\_scrt\_common\_main\_seh()   
0x00007ff8840626ad KERNEL32.DLL!UnknownFunction

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<div class="post-metadata">

**Author:** ![Kevin\_Ring](https://sea2.discourse-cdn.com/cesium/user_avatar/community.cesium.com/kevin_ring/32/2003_2.png) [@Kevin\_Ring](https://community.cesium.com/u/Kevin_Ring)\
**Post date:** [July 24, 2023, 4:13am UTC](https://community.cesium.com/t/lightmass-crashed/24692/4 "2023-07-24T04:13:47Z")

</div>

I just tried creating a new Game → Virtual Reality project in UE 5.1.1. Then I added the Cesium for Unreal plugin (v1.28.0) and restarted the Editor. No errors. There was initially an error related to the Water Plugin, but clicking the link in the error message fixed that easily. I also tried packaging, and that worked fine.

So… I need help reproducing this. Can anyone experiencing this please provide more detailed instructions on how to reproduce it?