SpeedTree model crash

LogPlayLevel: ERROR: System.ArgumentException: Staged filesystem reference may not start with a path separator or contain an empty path fragment (Etude2\Content\Arbres\2\Broadleaf_Desktop_Forest.uasset)
LogPlayLevel: à StagedFileSystemReference…ctor(String InName)
LogPlayLevel: à StagedFileReference…ctor(String Name)
LogPlayLevel: à Project.CreateStagingManifest(ProjectParams Params, DeploymentContext SC)
LogPlayLevel: à Project.CopyBuildToStagingDirectory(ProjectParams Params)
LogPlayLevel: à BuildCookRun.DoBuildCookRun(ProjectParams Params)
LogPlayLevel: à BuildCookRun.ExecuteBuild()
LogPlayLevel: à AutomationTool.BuildCommand.Execute()
LogPlayLevel: à AutomationTool.Automation.Execute(List1 CommandsToExecute, Dictionary2 Commands)
LogPlayLevel: à AutomationTool.Automation.Process(String[] Arguments)
LogPlayLevel: à AutomationTool.Program.MainProc(Object Param)
LogPlayLevel: à AutomationTool.InternalUtils.RunSingleInstance(Func`2 Main, Object Param)
LogPlayLevel: à AutomationTool.Program.Main()
LogPlayLevel: (see C:\Users\Alienware\AppData\Roaming\Unreal Engine\AutomationTool\Logs\C+Program+Files+Epic+Games+UE_4.19\UAT_Log.txt for full exception trace)
LogPlayLevel: AutomationTool exiting with ExitCode=1 (Error_Unknown)
LogPlayLevel: Completed Launch On Stage: Deploy Task, Time: 0.008768
LogPlayLevel: BUILD FAILED
PackagingResults: Error: Launch failed! Unknown Error
LogSlate: FSceneViewport::OnFocusLost() reason 0
LogSlate: FSceneViewport::OnFocusLost() reason 2
LogSlate: FSceneViewport::OnFocusLost() reason 2

When i’m using SpeedTree’s models on Unreal Engine I don’t Understand Why but when i package my game or when i launch this it said “Launch Error” and this probleme is from speedtree’s models can you help fort this ??