Thanks for the reply again! 
I download the unreal engine from the Epic Games Launcher, and i develope the game with blueprints…
This is the Swarm Agen log (the error message):
[Interface:OpenChannel] Error: System.IO.IOException: process cannot reach the file “C:\Users\balaz\AppData\Local\UnrealEngine\4.26\Saved\Swarm\SwarmCache\AgentStagingArea\v1.DA24ACD8274453AD26E158832695FF65ACE1853B.mtrlgz” because it is being used by another process.
in the following location: System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
in the following location: 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)
in the following location: System.IO.FileStream…ctor(String path, FileMode mode, FileAccess access, FileShare share)
in the following location: NSwarm.FSwarmInterface.OpenChannel(String ChannelName, EChannelFlags ChannelFlags) location: D:\Build++UE4\Sync\Engine\Saved\CsTools\Engine\Source\Editor\SwarmInterface\DotNET\SwarmInterface.cs, line: 1604