UnresolvedAssemblyException in Blend for VS design view ONLY - works fine in VS design view

.NET Framework: 4.5.1

I'm getting a curious error in Blend for visual studio 2015 which I cannot find the source of.

If I open my WPF solution in VS, it loads and runs fine. The design view also works.

However, if I open my WPF solution in Blend, whenever I open any of my .xaml files in the designer, they load briefly (for about a second)and then throw the following error:

Microsoft.MetadataReader.UnresolvedAssemblyException
Type universe cannot resolve assembly: System.Runtime, Version=4.0.0.0, 

Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a.
   at Microsoft.MetadataReader.SimpleUniverse.Microsoft.MetadataReader.ITypeUniverse.ResolveAssembly(AssemblyName name)
   at Microsoft.MetadataReader.SimpleUniverse.Microsoft.MetadataReader.ITypeUniverse.ResolveAssembly(Module scope, Token tokenAssemblyRef)
   at Microsoft.MetadataReader.MetadataOnlyModule.ResolveTypeRef(ITypeReference typeReference)
   at Microsoft.MetadataReader.MetadataOnlyTypeReference.GetResolvedTypeWorker()
   at Microsoft.MetadataReader.TypeProxy.GetResolvedType()
   at Microsoft.MetadataReader.TypeProxy.GetHashCode()
   at System.Collections.Generic.ObjectEqualityComparer`1.GetHashCode(T obj)
   at System.Collections.Concurrent.ConcurrentDictionary`2.TryGetValue(TKey key, TValue& value)
   at Microsoft.VisualStudio.DesignTools.XamlDesigner.Metadata.XamlPlatformMetadata.GetType(Type type)
   at Microsoft.VisualStudio.DesignTools.Platform.Metadata.TypeResolver.GetType(String key, IAssembly assembly, Type type)
   at Microsoft.VisualStudio.DesignTools.Platform.Metadata.TypeResolver.GetType(Type type)
   at Microsoft.VisualStudio.DesignTools.XamlDesigner.Metadata.XamlProjectMetadata.GetType(Type type)
   at Microsoft.VisualStudio.DesignTools.Platform.Metadata.ProjectContextType.Cache()
   at Microsoft.VisualStudio.DesignTools.Platform.Metadata.ProjectContextType.Initialize(IXmlNamespace xmlNamespace, Type type)
   at Microsoft.VisualStudio.DesignTools.XamlDesigner.Metadata.MockType.Initialize(IXmlNamespace xmlNamespace, Type type)
   at Microsoft.VisualStudio.DesignTools.Platform.Metadata.TypeResolver.GetType(String key, IAssembly assembly, Type type)
   at Microsoft.VisualStudio.DesignTools.Platform.Metadata.TypeResolver.GetType(Type type)
   at Microsoft.VisualStudio.DesignTools.XamlDesigner.Metadata.XamlProjectMetadata.GetType(Type type)
   at Microsoft.VisualStudio.DesignTools.Platform.Metadata.ProjectContextType.Cache()
   at Microsoft.VisualStudio.DesignTools.Platform.Metadata.ProjectContextType.Initialize(IXmlNamespace xmlNamespace, Type type)
   at Microsoft.VisualStudio.DesignTools.XamlDesigner.Metadata.MockType.Initialize(IXmlNamespace xmlNamespace, Type type)
   at Microsoft.VisualStudio.DesignTools.Platform.Metadata.TypeResolver.GetType(String key, IAssembly assembly, Type type)
   at Microsoft.VisualStudio.DesignTools.Platform.Metadata.TypeResolver.GetType(Type type)
   at Microsoft.VisualStudio.DesignTools.XamlDesigner.Metadata.XamlProjectMetadata.GetType(Type type)
   at Microsoft.VisualStudio.DesignTools.XamlDesigner.Tools.Assets.AssemblyAssetProvider.SynchronizedInitialize()
   at Microsoft.VisualStudio.DesignTools.XamlDesigner.Tools.Assets.AssemblyAssetProvider.UpdateAssets()
   at Microsoft.VisualStudio.DesignTools.Designer.Tools.Assets.AssetProvider.Update()
   at Microsoft.VisualStudio.DesignTools.Designer.Tools.Assets.AssetLibrary.UpdateAssetProvidersWorker()
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
   at System.Windows.Threading.DispatcherOperation.InvokeImpl()
   at System.Windows.Threading.DispatcherOperation.InvokeInSecurityContext(Object state)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Windows.Threading.DispatcherOperation.Invoke()
   at System.Windows.Threading.Dispatcher.ProcessQueue()
   at System.Windows.Threading.Dispatcher.WndProcHook(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
   at System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs)
   at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)
   at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg)
   at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame)
   at System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame)
   at System.Windows.Threading.DispatcherOperation.Wait(TimeSpan timeout)
   at System.Windows.Threading.Dispatcher.InvokeImpl(DispatcherOperation operation, CancellationToken cancellationToken, TimeSpan timeout)
   at System.Windows.Threading.Dispatcher.Invoke(Action callback, DispatcherPriority priority, CancellationToken cancellationToken, TimeSpan timeout)
   at System.Windows.Threading.Dispatcher.Invoke(Action callback, DispatcherPriority priority)
   at Microsoft.VisualStudio.DesignTools.Platform.Utility.UIThreadDispatcherHelper.Invoke(DispatcherPriority dispatcherPriority, Action action)
   at Microsoft.VisualStudio.DesignTools.Designer.View.DesignTimeResourceResolver.Resolve(IDocumentContext documentContext, EditDesignTimeResourceModelMode mode, String missingResourceName) ........etc

If I debug this in Visual studio (attach to the blend.exe process) I get the following error:

Exception thrown: 'System.IO.DirectoryNotFoundException' in mscorlib.dll

Additional information: Could not find a part of the path '<path to my project>\Design\projectGuides.guides'.

This "Design" folder doesn't exist and I don't know where it's getting requested from. I dont have any guides defined across my entire project or anything like that.

Also, I can't see any connection between these two messages.

Any tips or ideas would be greatly appreciated!

Solution

Solution

So the solution to this became clear when I updated to .NET framework 4.6. The Exception became something that returned something useful in a search:

Cannot add additional fields to a type that does not have a constructor

The first result when I searched for this was Corrado's Blog, where I was directed to a setting in Tools > Options > XAML designer, and then tick the "Run project code in XAML Designer (if supported)" option.

No problems since then. Hope this helps someone else at some point.