Hello!

Have you encountered the “Swarm Failed to Kick Off” error on an Unreal Engine project when trying to build a level? I did, after we switched to a custom engine build. Since most of the resources on the web were not helpful. Here’s a really simply fix that may work for you.

(Step 3 is the most important. I did the first two steps, but they may be unnecessary. Back up any files you want kept!)

1. Delete the stuff in this folder (or equivalent location – wherever your engine is installed.)

E:\UE4_14\UnrealEngine-4.14\Engine\Saved\Swarm\SwarmCache

2. Delete all the stuff in this folder (or equivalent for your engine version.)

C:\Users\YOURWindowsUser\AppData\Local\UnrealEngine\4.14

3. Open the UE4.sln file in your engine install folder.

Build UnrealLightmass. Once this is done, run the editor and you should be able to build your levels again.

That last step should almost certainly resolve your issue. If not, there are other solutions on the net, but this is the one that fixed it for me.

Hope that helps somebody out there!

— Zag

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