# Swarm Agent - Failed to cache the executable

**URL:** <https://forums.unrealengine.com/t/swarm-agent-failed-to-cache-the-executable/351770>\
**Category:** Asset Creation\
**Tags:** swarm, lighting-build, unreal-engine, question\
**Created:** [March 25, 2016, 6:04pm UTC](https://forums.unrealengine.com/t/swarm-agent-failed-to-cache-the-executable/351770 "2016-03-25T18:04:54Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Metathesus](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Metathesus](https://forums.unrealengine.com/u/Metathesus)\
**Post date:** [March 25, 2016, 6:04pm UTC](https://forums.unrealengine.com/t/swarm-agent-failed-to-cache-the-executable/351770/1 "2016-03-25T18:04:54Z")

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Hello,

I can’t build light.  
Here the log of the swarm agent

```
18:54:23: [Interface:TryOpenConnection] Local connection established
18:54:26: [Job] Accepted Job C0183CE7-4F8EDA92-956A0D92-6CD6D252
18:54:28: [Interface:CacheAllFiles] Failed to cache the executable: C:\Unreal Engine 4.11\Engine\Binaries\Win64\UnrealLightmass.exe
18:54:35: [Job] AddTask: Rejected, cannot add a task to a running job
18:54:35: [CloseConnection] Closing connection 1E883796 using handle 1E883796
18:54:35: [CloseConnection] Connection confirmed for disconnection 1E883796
18:54:35: [CloseConnection] Closing orphaned Job (C0183CE7-4F8EDA92-956A0D92-6CD6D252)
18:54:35: [CloseConnection] Connection disconnected 1E883796
18:54:35: [GetMessage] Safely returning to 1E883796 with no message
18:54:36: [MaintainConnections] Local connection has closed (1E883796)
18:54:36: [MaintainConnections] Removed connection 1E883796
18:54:36: [MaintainConnections] All connections have closed

```

I have exactly the same config of swarm agents of UE4.10 where the problem doesn’t occur.

My project is the same than 4.10, I have just made changes on 3 materials after my really fresh migration to preview 8.

Tell me if you need other logs.

Thanks for your help and advises.

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<div class="post-metadata">

**Author:** ![Metathesus](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Metathesus](https://forums.unrealengine.com/u/Metathesus)\
**Post date:** [March 25, 2016, 6:18pm UTC](https://forums.unrealengine.com/t/swarm-agent-failed-to-cache-the-executable/351770/2 "2016-03-25T18:18:55Z")

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Oups!!!  
Sorry for disturbing! Answer Here:  
[[Swarm won't start. Won't build lighting - C++ - Unreal Engine Forums](https://forums.unrealengine.com/showthread.php?104087-Swarm-won-t-start-Won-t-build-lighting)][1]

[1]

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**Author:** ![JonathanArmstrong](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@JonathanArmstrong](https://forums.unrealengine.com/u/JonathanArmstrong)\
**Post date:** [April 1, 2021, 9:25am UTC](https://forums.unrealengine.com/t/swarm-agent-failed-to-cache-the-executable/351770/3 "2021-04-01T09:25:33Z")

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Thanks @Metathesus , that did it. There is also documentation, here, about the source engine version of UE needing to have Lightmass compiled from Visual Studio, quite commonly. Gives a lot of other Lightmass troubleshooting tips, as well.

> **[Unreal Swarm](https://docs.unrealengine.com/4.27/en-US/RenderingAndGraphics/Lightmass/UnrealSwarmOverview/)**
>
> An overview of Unreal Swarm, our task distribution system for computationally expensive applications, including Unreal Lightmass, the high-quality static global illumination solver in Unreal Engine 4.