Ich habe eine benutzerdefinierte msbuild-Aufgabe mit diesem Befehl:

var workspace = Workspace.LoadStandAloneProject(csprojPath);

Wenn ich es ausführe, wird der folgende Fehler ausgegeben:

  System.InvalidCastException was unhandled by user code
  Message=Unable to cast transparent proxy to type 'Roslyn.Utilities.SerializableDataStorage'.
  Source=Roslyn.Services
  StackTrace:
       at Roslyn.Utilities.RemoteServices.CreateInstance[T]()
       at Roslyn.Services.Host.TemporaryStorageServiceFactory.CreateService(IWorkspaceServiceProvider workspaceServices)
       at Roslyn.Services.Host.WorkspaceServiceProviderFactory.Provider.c__DisplayClass7.b__4()
       at Roslyn.Utilities.NonReentrantLazy`1.get_Value()
       at Roslyn.Services.Host.WorkspaceServiceProviderFactory.Provider.GetService[TWorkspaceService]()
       at Roslyn.Services.SolutionServices..ctor(IWorkspaceServiceProvider workspaceServices, ILanguageServiceProviderFactory languageServicesFactory)
       at Roslyn.Services.Solution..ctor(SolutionId id, String filePath, VersionStamp version, VersionStamp latestProjectVersion, ILanguageServiceProviderFactory languageServiceProviderFactory, IWorkspaceServiceProvider workspaceServices)
       at Roslyn.Services.Host.SolutionFactoryServiceFactory.SolutionFactoryService.CreateSolution(SolutionId id)
       at Roslyn.Services.Host.TrackingWorkspace.CreateNewSolution(ISolutionFactoryService solutionFactory, SolutionId id)
       at Roslyn.Services.Host.TrackingWorkspace..ctor(IWorkspaceServiceProvider workspaceServiceProvider, Boolean enableBackgroundCompilation, Boolean enableInProgressSolutions)
       at Roslyn.Services.Host.HostWorkspace..ctor(IWorkspaceServiceProvider workspaceServiceProvider, Boolean enableBackgroundCompilation, Boolean enableInProgressSolutions, Boolean enableFileTracking)
       at Roslyn.Services.Host.LoadedWorkspace..ctor(ILanguageServiceProviderFactory languageServiceProviderFactory, IWorkspaceServiceProvider workspaceServiceProvider, IProjectFileService projectFileFactsService, IDictionary`2 globalProperties, Boolean enableBackgroundCompilation, Boolean enableFileTracking)
       at Roslyn.Services.Host.LoadedWorkspace..ctor(ExportProvider exportProvider, Boolean solutionLoadOnly, Boolean enableFileTracking)
       at Roslyn.Services.Host.LoadedWorkspace..ctor(Boolean enableFileTracking)
       at Roslyn.Services.Host.LoadedWorkspace.LoadStandAloneProject(String projectFileName, String configuration, String platform, String language, Boolean enableFileTracking)
       at Roslyn.Services.Workspace.LoadStandAloneProject(String projectFileName, String configuration, String platform, String language, Boolean enableFileTracking)
       ...

Wenn derselbe Code in einer Konsolenanwendung mit demselben Projekt ausgeführt wird, funktioniert er einwandfrei.

Irgendwelche Ideen? Googeln war nicht hilfreich!