Estoy ejecutando VS 2010 junto con Expression Blend 4 beta. Creé un proyecto MVVM Light a partir de las plantillas suministradas y obtengo una excepción System.IO.FileLoadException cuando intento ver MainWindow.Xaml en la ventana del diseñador VS 2010. La plantilla ya hace referencia a System.Windows.Interactivity. Aquí están los detalles de la excepción:

System.IO.FileLoadException
Could not load file or assembly 'System.Windows.Interactivity, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. Operation is not supported. (Exception from HRESULT: 0x80131515)
   at System.Reflection.RuntimeAssembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks)
   at System.Reflection.RuntimeAssembly.nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, RuntimeAssembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection, Boolean suppressSecurityChecks)
   at System.Reflection.RuntimeAssembly.InternalLoadAssemblyName(AssemblyName assemblyRef, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection, Boolean suppressSecurityChecks)
   at System.Reflection.Assembly.Load(AssemblyName assemblyRef)
   at MS.Internal.Package.VSIsolationProviderService.RemoteReferenceProxy.VsReflectionResolver.GetRuntimeAssembly(Assembly reflectionAssembly)
   at Microsoft.Windows.Design.Metadata.ReflectionMetadataContext.CachingReflectionResolver.GetRuntimeAssembly(Assembly reflectionAssembly)
   at Microsoft.Windows.Design.Metadata.ReflectionMetadataContext.Microsoft.Windows.Design.Metadata.IReflectionResolver.GetRuntimeAssembly(Assembly reflectionAssembly)
   at MS.Internal.Metadata.ClrAssembly.GetRuntimeMetadata(Object reflectionMetadata)
   at Microsoft.Windows.Design.Metadata.AttributeTableContainer.<MergeAttributesIterator>d__c.MoveNext()
   at Microsoft.Windows.Design.Metadata.AttributeTableContainer.GetAttributes(Assembly assembly, Type attributeType, Func`2 reflectionMapper)
   at MS.Internal.Metadata.ClrAssembly.GetAttributes(ITypeMetadata attributeType)
   at MS.Internal.Design.Metadata.Xaml.XamlAssembly.get_XmlNamespaceCompatibilityMappings()
   at Microsoft.Windows.Design.Metadata.Xaml.XamlExtensionImplementations.GetXmlNamespaceCompatibilityMappings(IAssemblyMetadata sourceAssembly)
   at Microsoft.Windows.Design.Metadata.Xaml.XamlExtensions.GetXmlNamespaceCompatibilityMappings(IAssemblyMetadata source)
   at MS.Internal.Design.Metadata.ReflectionProjectNode.BuildSubsumption()
   at MS.Internal.Design.Metadata.ReflectionProjectNode.SubsumingNamespace(Identifier identifier)
   at MS.Internal.Design.Markup.XmlElement.BuildScope(PrefixScope parentScope, IParseContext context)
   at MS.Internal.Design.Markup.XmlElement.ConvertToXaml(XamlElement parent, PrefixScope parentScope, IParseContext context, IMarkupSourceProvider provider)
   at MS.Internal.Design.DocumentModel.DocumentTrees.Markup.XamlSourceDocument.FullParse(Boolean convertToXamlWithErrors)
   at MS.Internal.Design.DocumentModel.DocumentTrees.Markup.XamlSourceDocument.get_RootItem()
   at Microsoft.Windows.Design.DocumentModel.Trees.ModifiableDocumentTree.get_ModifiableRootItem()
   at Microsoft.Windows.Design.DocumentModel.MarkupDocumentManagerBase.get_LoadState()
   at MS.Internal.Host.PersistenceSubsystem.Load()
   at MS.Internal.Host.Designer.Load()
   at MS.Internal.Designer.VSDesigner.Load()
   at MS.Internal.Designer.VSIsolatedDesigner.VSIsolatedView.Load()
   at MS.Internal.Designer.VSIsolatedDesigner.VSIsolatedDesignerFactory.Load(IsolatedView view)
   at MS.Internal.Host.Isolation.IsolatedDesigner.BootstrapProxy.LoadDesigner(IsolatedDesignerFactory factory, IsolatedView view)
   at MS.Internal.Host.Isolation.IsolatedDesigner.BootstrapProxy.LoadDesigner(IsolatedDesignerFactory factory, IsolatedView view)
   at MS.Internal.Host.Isolation.IsolatedDesigner.Load()
   at MS.Internal.Designer.DesignerPane.LoadDesignerView()

System.NotSupportedException Se intentó cargar un ensamblado desde una ubicación de red, lo que habría provocado que el ensamblado se protegiera en versiones anteriores de .NET Framework. Esta versión de .NET Framework no habilita la política CAS por defecto, por lo que esta carga puede ser peligrosa. Si esta carga no está destinada a proteger el ensamblaje, active el conmutador loadFromRemoteSource. Verhttp://go.microsoft.com/fwlink/?LinkId=155569 para más información.