Swarm failed to kick off (4.11.2)

In one map, in one project, I can’t build the lighting. I tried to copy-paste everything in a new fresh level and it doesn’t work. Other maps in the same project, with almost the same assets are building correctly tho! I have a lightmass importance volume. Here’s the message I get in the swarm agent log :

12:08:39 PM: [Interface:OpenChannel] Error: System.IO.IOException: The process cannot access the file ‘C:\Users\Philippe\AppData\Local\UnrealEngine\4.11\Saved\Swarm\SwarmCache\AgentStagingArea\8487AD2E5DBA413C81373D29B2915895.7C0FB2FB4F5E5D8CB27AAFA5A53F1599.mtrlgz’ because it is being used by another process.
at System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)
at System.IO.FileStream…ctor(String path, FileMode mode, FileAccess access, FileShare share)
at NSwarm.FSwarmInterface.OpenChannel(String ChannelName, EChannelFlags ChannelFlags) in i:\Perforce2\UE4-Orion\Engine\Source\Editor\SwarmInterface\DotNET\SwarmInterface.cs:line 160

Hey heartlessphil,

Try cleaning your Swarm Agent cache as well as taking a look at our Swarm Agent Troubleshooting Guide to see if you can find any helpful solutions there as well.

Cheers,