I have seen similar posts with this error, but all seem to be resolved with deleting binaries and generating project files and rebuilding or something along those lines. However, I seem to have tried all of these things and even created a new fresh project with just a single cpp and header file and still getting the issue.
It looks like one of the first errors coming up after the WaitMutex FromMsBuild line is:
The requested operation cannot be performed on a file with a user-mapped section open. : ‘C:\Unreal\MyProject\Intermediate\Build\BuildRules\MyProjectModuleRules.dll’
I saw some people seem to get by this by running UE5 as admin but that hasn’t worked either.
Plz help
1>------ Build started: Project: MyProject, Configuration: Development_Editor x64 ------
1>Using bundled DotNet SDK version: 6.0.302
1>Running UnrealBuildTool: dotnet “…..\Engine\Binaries\DotNET\UnrealBuildTool\UnrealBuildTool.dll” MyProjectEditor Win64 Development -Project=“C:\Unreal\MyProject\MyProject.uproject” -WaitMutex -FromMsBuild
1>Log file: C:\Users\purpl\AppData\Local\UnrealBuildTool\Log.txt
1>Creating makefile for MyProjectEditor (.uproject file is newer)
1>Total execution time: 0.98 seconds
1>Unhandled exception: System.IO.IOException: The requested operation cannot be performed on a file with a user-mapped section open. : ‘C:\Unreal\MyProject\Intermediate\Build\BuildRules\MyProjectModuleRules.dll’
1> at Microsoft.Win32.SafeHandles.SafeFileHandle.CreateFile(String fullPath, FileMode mode, FileAccess access, FileShare share, FileOptions options)
1> at Microsoft.Win32.SafeHandles.SafeFileHandle.Open(String fullPath, FileMode mode, FileAccess access, FileShare share, FileOptions options, Int64 preallocationSize)
1> at System.IO.Strategies.OSFileStreamStrategy…ctor(String path, FileMode mode, FileAccess access, FileShare share, FileOptions options, Int64 preallocationSize)
1> at System.IO.Strategies.FileStreamHelpers.ChooseStrategyCore(String path, FileMode mode, FileAccess access, FileShare share, FileOptions options, Int64 preallocationSize)
1> at System.IO.Strategies.FileStreamHelpers.ChooseStrategy(FileStream fileStream, String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options, Int64 preallocationSize)
1> at UnrealBuildTool.DynamicCompilation.CompileAssembly(FileReference OutputAssemblyPath, IEnumerable1 SourceFileNames, ILogger Logger, IEnumerable1 ReferencedAssembies, IEnumerable1 PreprocessorDefines, Boolean TreatWarningsAsErrors) in C:\Program Files\Epic Games\UE_5.3\Engine\Source\Programs\UnrealBuildTool\System\DynamicCompilation.cs:line 258 1> at UnrealBuildTool.DynamicCompilation.CompileAndLoadAssembly(FileReference OutputAssemblyPath, IEnumerable1 SourceFileNames, ILogger Logger, IEnumerable1 ReferencedAssembies, IEnumerable1 PreprocessorDefines, Boolean DoNotCompile, Boolean ForceCompile, Boolean TreatWarningsAsErrors) in C:\Program Files\Epic Games\UE_5.3\Engine\Source\Programs\UnrealBuildTool\System\DynamicCompilation.cs:line 341
1> at UnrealBuildTool.RulesAssembly…ctor(RulesScope Scope, IReadOnlyList1 BaseDirs, IReadOnlyList1 Plugins, IReadOnlyDictionary2 ModuleFileToContext, IReadOnlyList1 TargetFiles, FileReference AssemblyFileName, Boolean bContainsEngineModules, Nullable1 DefaultBuildSettings, Boolean bReadOnly, Boolean bSkipCompile, Boolean bForceCompile, RulesAssembly Parent, ILogger Logger) in C:\Program Files\Epic Games\UE_5.3\Engine\Source\Programs\UnrealBuildTool\System\RulesAssembly.cs:line 141 1> at UnrealBuildTool.RulesCompiler.<>c__DisplayClass9_0.<CreateProjectRulesAssembly>b__0(FileReference _) in C:\Program Files\Epic Games\UE_5.3\Engine\Source\Programs\UnrealBuildTool\System\RulesCompiler.cs:line 320 1> at System.Collections.Concurrent.ConcurrentDictionary2.GetOrAdd(TKey key, Func2 valueFactory) 1> at UnrealBuildTool.RulesCompiler.CreateProjectRulesAssembly(FileReference ProjectFileName, Boolean bUsePrecompiled, Boolean bSkipCompile, Boolean bForceCompile, ILogger Logger) in C:\Program Files\Epic Games\UE_5.3\Engine\Source\Programs\UnrealBuildTool\System\RulesCompiler.cs:line 235 1> at UnrealBuildTool.RulesCompiler.CreateTargetRulesAssembly(FileReference ProjectFile, String TargetName, Boolean bSkipRulesCompile, Boolean bForceRulesCompile, Boolean bUsePrecompiled, FileReference ForeignPlugin, Boolean bBuildPluginAsLocal, ILogger Logger) in C:\Program Files\Epic Games\UE_5.3\Engine\Source\Programs\UnrealBuildTool\System\RulesCompiler.cs:line 407 1> at UnrealBuildTool.UEBuildTarget.Create(TargetDescriptor Descriptor, Boolean bSkipRulesCompile, Boolean bForceRulesCompile, Boolean bUsePrecompiled, UnrealIntermediateEnvironment IntermediateEnvironment, ILogger Logger) in C:\Program Files\Epic Games\UE_5.3\Engine\Source\Programs\UnrealBuildTool\Configuration\UEBuildTarget.cs:line 1257 1> at UnrealBuildTool.BuildMode.CreateMakefileAsync(BuildConfiguration BuildConfiguration, TargetDescriptor TargetDescriptor, ISourceFileWorkingSet WorkingSet, ILogger Logger) in C:\Program Files\Epic Games\UE_5.3\Engine\Source\Programs\UnrealBuildTool\Modes\BuildMode.cs:line 1114 1> at UnrealBuildTool.BuildMode.BuildAsync(List1 TargetDescriptors, BuildConfiguration BuildConfiguration, ISourceFileWorkingSet WorkingSet, BuildOptions Options, FileReference WriteOutdatedActionsFile, ILogger Logger, Boolean bSkipPreBuildTargets) in C:\Program Files\Epic Games\UE_5.3\Engine\Source\Programs\UnrealBuildTool\Modes\BuildMode.cs:line 396
1> at UnrealBuildTool.BuildMode.ExecuteAsync(CommandLineArguments Arguments, ILogger Logger) in C:\Program Files\Epic Games\UE_5.3\Engine\Source\Programs\UnrealBuildTool\Modes\BuildMode.cs:line 252
1> at UnrealBuildTool.UnrealBuildTool.Main(String ArgumentsArray) in C:\Program Files\Epic Games\UE_5.3\Engine\Source\Programs\UnrealBuildTool\UnrealBuildTool.cs:line 659
1>C:\Program Files\Microsoft Visual Studio\2022\Community\MSBuild\Microsoft\VC\v170\Microsoft.MakeFile.Targets(44,5): error MSB3073: The command ““C:\Program Files\Epic Games\UE_5.3\Engine\Build\BatchFiles\Build.bat” MyProjectEditor Win64 Development -Project=“C:\Unreal\MyProject\MyProject.uproject” -WaitMutex -FromMsBuild” exited with code 6.
1>Done building project “MyProject.vcxproj” – FAILED.