I am using Visual Studio 2012 Professional(using C#/XAML for windows 8 apps development).
WPF designer fails to load showing : An unhandled Exception has occured.
Details: System.ArgumentNullException Value cannot be null. Parameter name: key at System.Collections.Generic.Dictionary2.Insert(TKey
key, TValue value, Boolean add) at Microsoft.Expression.DesignModel.Metadata.PlatformMetadataBase.NewReplacedExternalType(PlatformMetadataBase platformMetadata, IPlatformTypes sourcePlatformTypes, IAssembly assembly, Type keyType, Type replaceType, ITypeId
baseType, ITypeId neutralType, IXmlNamespace xmlNamespace, String clrNamespace, AttributeCollection attributes, ProxyPropertyDescription[] properties) at Microsoft.Expression.DesignModel.Metadata.PlatformMetadataBase.NewReplacedExternalType(PlatformMetadataBase
platformMetadata, IPlatformTypes sourcePlatformTypes, IAssembly assembly, Type keyType, Type replaceType, ITypeId baseType, ITypeId neutralType, IXmlNamespace xmlNamespace, String clrNamespace, ProxyPropertyDescription[] properties) at Microsoft.Expression.WindowsXamlPlatform.WindowsUIXamlPlatformMetadata.OnInitialize()
at Microsoft.Expression.WindowsXamlPlatform.WindowsUIXamlPlatform.Initialize() at Microsoft.Expression.Platform.PlatformCreatorBase.CreatePlatform(IPlatformReferenceAssemblyResolver referenceAssemblyResolver) at Microsoft.Expression.DesignSurface.Project.ProjectContextBase.Initialize()
at Microsoft.Expression.DesignSurface.Project.XamlProjectContext.Initialize() at Microsoft.Expression.DesignSurface.Project.ProjectContextManager.GetProjectContext(IHostProject project, IPlatform platform, Boolean create) at Microsoft.Expression.DesignSurface.Project.ProjectContextManager.GetSourceItemContext(IHostSourceItem
sourceItem) at Microsoft.Expression.DesignSurface.DesignerService.CreateDesigner(IHostSourceItem item, IHostTextEditor editor, CancellationToken cancelToken) at Microsoft.Expression.DesignHost.Isolation.Remoting.RemoteDesignerService.<>c__DisplayClass10.<>c__DisplayClass12.<Microsoft.Expression.DesignHost.Isolation.Remoting.IRemoteDesignerService.CreateDesigner>b__f(CancellationToken
cancelToken) at Microsoft.Expression.DesignHost.Isolation.Remoting.RemoteDesignerService.CallWithCancellation[TResult](IRemoteCancellationToken remoteToken, Func2 func) at Microsoft.Expression.DesignHost.Isolation.Remoting.RemoteDesignerService.<>c_DisplayClass10.b_e()
at Microsoft.Expression.DesignHost.Isolation.Remoting.ThreadMarshaler.<>c_DisplayClass16`1.b_15() at Microsoft.Expression.DesignHost.Isolation.Remoting.STAMarshaler.Call.InvokeWorker()
System.ArgumentNullException Value cannot be null. Parameter name: key
Server stack trace: at Microsoft.Expression.DesignHost.Isolation.Remoting.STAMarshaler.WaitForCompletion(NestedCallContext nestedCallContext, BlockingCall call, WaitHandle timeoutSignal) at Microsoft.Expression.DesignHost.Isolation.Remoting.STAMarshaler.MarshalIn(Action action, Int32 targetApartmentId) at Microsoft.Expression.DesignHost.Isolation.Remoting.ThreadMarshaler.MarshalIn(IRemoteObject targetObject, Action action) at Microsoft.Expression.DesignHost.Isolation.Remoting.ThreadMarshaler.MarshalIn[TResult](IRemoteObject targetObject, Func`1 func) at Microsoft.Expression.DesignHost.Isolation.Remoting.RemoteDesignerService.Microsoft.Expression.DesignHost.Isolation.Remoting.IRemoteDesignerService.CreateDesigner(IRemoteHostSourceItem remoteItem, IRemoteHostTextEditor remoteEditor, IRemoteCancellationToken remoteToken) at System.Runtime.Remoting.Messaging.StackBuilderSink._PrivateProcessMessage(IntPtr md, Object[] args, Object server, Object[]& outArgs) at System.Runtime.Remoting.Messaging.StackBuilderSink.SyncProcessMessage(IMessage msg)
Exception rethrown at [0]: at System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg) at System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type) at Microsoft.Expression.DesignHost.Isolation.Remoting.IRemoteDesignerService.CreateDesigner(IRemoteHostSourceItem remoteItem, IRemoteHostTextEditor remoteEditor, IRemoteCancellationToken cancelToken) at Microsoft.Expression.DesignHost.Isolation.Remoting.LocalDesignerService.<>c_DisplayClass8.b_6(IRemoteDesignerService d) at Microsoft.Expression.DesignHost.Isolation.Remoting.ThreadMarshaler.<>c_DisplayClass4`2.b_3() at Microsoft.Expression.DesignHost.Isolation.Remoting.STAMarshaler.Call.InvokeWorker()
System.ArgumentNullException Value cannot be null. Parameter name: key at Microsoft.Expression.DesignHost.Isolation.Remoting.STAMarshaler.WaitForCompletion(NestedCallContext nestedCallContext, BlockingCall call, WaitHandle timeoutSignal) at Microsoft.Expression.DesignHost.Isolation.Remoting.STAMarshaler.MarshalOutSynchronous(Action
action, Int32 targetApartmentId, WaitHandle aborted, WaitHandle timeoutSignal) at Microsoft.Expression.DesignHost.Isolation.Remoting.STAMarshaler.MarshalOut(Action action, Int32 targetApartmentId, WaitHandle aborted, CallSynchronizationMode syncMode, WaitHandle
timeoutSignal) at Microsoft.Expression.DesignHost.Isolation.Remoting.ThreadMarshaler.MarshalOut[TValue](RemoteHandle1
targetObject, Action action, CallSynchronizationMode syncMode) at Microsoft.Expression.DesignHost.Isolation.Remoting.ThreadMarshaler.MarshalOut[TResult,TValue](RemoteHandle1 targetObject, Func2
func, CallSynchronizationMode syncMode) at Microsoft.Expression.DesignHost.Isolation.Remoting.LocalDesignerService.CreateDesignerImpl(IHostSourceItem item, IHostTextEditor editor, RemoteCancellationToken remoteCancelToken) at Microsoft.Expression.DesignHost.Isolation.Remoting.LocalDesignerService.<>c__DisplayClass12.<Microsoft.Expression.DesignHost.IDesignerService.CreateDesigner>b__11(RemoteCancellationToken
remoteToken) at Microsoft.Expression.DesignHost.Isolation.Remoting.LocalDesignerService.CallWithCancellation[TResult](CancellationToken cancelToken, Func2 func) at Microsoft.Expression.DesignHost.Isolation.Remoting.LocalDesignerService.Microsoft.Expression.DesignHost.IDesignerService.CreateDesigner(IHostSourceItem
item, IHostTextEditor editor, CancellationToken cancelToken) at Microsoft.Expression.DesignHost.IsolatedDesignerService.IsolatedDesignerView.CreateDesignerViewInfo(CancellationToken cancelToken)