could also use some help with this issue. thanks!
I upgraded to Unreal 4.7, and while I was doing a lighting build, I ran into some lighting build errors saying lightmass crashed array index out of bounds. Its only happening on adding certain static meshes and not all. I have looked the properties of meshes that work and meshes that don’t, and there is no difference. Can anyone help in figuring out what is wrong with these meshes? This is really urgent!
Ya all a few of my assests have done this too. really hard goign threw each one and find what ones killing my lighting builds.
Yep, I have had this problem recently and dont know how to fix it! Please help!
GDC is in 3 days…HELP urgently needed
Help! Please!!
Hi SiddG,
Did you ever get this sorted?
Often with Lightmass there can be several different reasons for the errors that come up. At the moment I’m in the process of getting a general troubleshooting and tips guide up for lightmass on our Wiki here: A new, community-hosted Unreal Engine Wiki - Announcements - Epic Developer Community Forums
It’s still at least a week out before it’ll be up though.
Some of the common things that can cause Lightmass to crash are:
- Lightmap resolution size too high for lots of objects
- Hardware limitations, specifically not enough RAM, as Lightmass is a heavy process.
- Clearing derived data cache can help as well: X: / Users / [ Computer name ] / AppData / Local / UnrealEngine/ - Delete everything in this folder.
- Open Swarm Agent > Menu > Cache > Click Clean and Click Validate.
- Having multiple Swarm Agents open (check taskbar) will cause issues or failure to build
If this is a specific mesh causing lightmass to crash when in only included in the scene I’d be interested in having a look at the asset if possible. I’ve not run across that specific issue.
Let me know.
Tim
It was being caused by certain specific assets. Re-exporting them from Maya and then re-importing them into Unreal fixed them. I believe we over-wrote all the asset files, but I’ll see if I can find an older, broken version to send you.
If you get an asset that does this I’d be glad to test and get this reported. It seems very odd for a specific mesh to crash lightmass like that. Usually it’s some other contributing factors rather than a single asset, but if it’s reproducible and happens when in the scene but not when removed that’d be intriguing.
Thanks and let me know if you get an asset that does this! 
I have a copy of one of the assets that caused this. The light build fails only if that asset is in scene, and succeeds if I remove it. I’m unable to upload it here because it says “file type invalid”
Thanks for getting back to me SiddG!
You can place it in a zip file and upload here or you can send it privately in a zip to me on the forums if you’d like. Either way will work so long as the attachment is under 5.2 mb. If it’s over that you can post a link to dropbox or google drive to share.
Thanks!
hmm…I’ve just tried this and am not seeing lighting not build on my end.
Everything appears to check out:
Can you copy the log that lightmass prints in Swarm Agent to a txt file and post here? That may have something useful.
Hey there,
I’d the same problem. The problem causer was a static mesh. It was a 3d model of the asteroid Eros Gaskel. It was originally a Stl file. I’ve imported it to Blender and exported it as an fbx. After that I’ve imported it as a static mesh into UE4. I had to save the level under a different name and did delete piece after piece and build over and over again in order to evaluate what mesh caused the problem. I’m kind of a noob, so I don’t have any idea what caused the fbx to crash the lightning. I had no special options defined in the detail panel or something like that. It was just a very comon static mesh, like I’ve already hundreds of them hanging around in all my levels. All I can say, it was the first time I was using a Stl file.
Hope that helps in some way…
Hi guys,
I’ve got the same error. I’ve imported a chair model from 3dsmax using datasmith. After that, I wanted to make the same chair to look like a bar chair so I edited the same model in 3dsmax (made the chair with longer legs) and imported it into the same scene. Then I’ve built lightning and got this “Array Index out of Bounds” error. I fixed it by remaining all the meshes of the newly imported bar chair. I think this error occurred to me than there were two meshes with the same name but with different geometry.
Hope it helps
Had a similar issue, the static mesh causing me problems was either an Unreal cube or cylinder. Im using level streaming, and had moved the cylinder from one level to another between bakes. Fixed by removing them and replacing them other other objects, then rebuilding. I suspect the moving objects between levels between bakes was the problem?