Swarm IOException - can't build lightmap

[Interface:OpenChannel] Error: System.IO.IOException: The process cannot access the file ‘C:\Users\Expressive\AppData\Local\UnrealEngine\5.3\Saved\Swarm\SwarmCache\AgentStagingArea\v2.78377A59B5528BC04AB2E9118FF8B19EE0A6F484.F1D9D1273D5C02B018C5337E52EE45E707771904.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 D:\build++UE5\Sync\Engine\Saved\CsTools\Engine\Source\Editor\SwarmInterface\DotNET\SwarmInterface.cs:line 1604

this is my swarm agents error message, I’m using ue 5.3. actually its a ancient city with 50 unique building and others element. and i think the problem started when i upgrade the project from ue4.26 to 5.1. still i cannot solve it. can someone help?