I just downloaded and installed the EO code so no modifications have been made to the code.

Yet, MainWindow.xaml in the sample C# TabbedBrowser project is throwing an exception when opened in the Visual Studio 2013 Designer.

The same error occurs in the VB sample project, also.

Please advise on how to fix.

Here are the details:

System.ArgumentException
An item with the same key has already been added.
at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource)
at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
at Microsoft.Expression.DesignModel.Metadata.MemberCollection.get_FieldIndex()
at Microsoft.Expression.DesignModel.Metadata.MemberCollection.CreateField(String fieldName, MemberKey& key)
at Microsoft.Expression.DesignModel.Metadata.MemberCollection.CreateMember(MemberType memberTypes, String memberName, MemberKey& key)
at Microsoft.Expression.DesignModel.Metadata.MemberCollection.TryGetCachedMember(MemberType memberTypes, String memberName, Boolean create, IMember& member)
at Microsoft.Expression.DesignModel.Metadata.MemberCollection.GetMember(MemberType memberTypes, String memberName, MemberAccessTypes access)
at Microsoft.Expression.DesignModel.Metadata.ProjectContextType.GetMember(MemberType memberTypes, String memberName, MemberAccessTypes access)
at Microsoft.Expression.Markup.XamlTypeHelper.GetPropertyKey(XamlParserContext parserContext, ITextLocation lineInformation, XmlNamespace xmlNamespace, String typeAndPropertyName, XmlNamespace targetTypeNamespace, IType targetTypeId, MemberType memberTypes, MemberType defaultType, Boolean allowProtectedPropertiesOnTargetType)
at Microsoft.Expression.Markup.XamlParser.GetPropertyKey(XamlParserContext parserContext, XmlElementReference xmlElementReference, XmlElement xmlElement, XmlAttribute attribute, IType targetType, Boolean allowProtectedPropertiesOnTargetType, IProperty& propertyKey)
at Microsoft.Expression.Markup.XamlParser.AddPropertiesAndChildren(XamlParserContext parserContext, DocumentCompositeNodeReference nodeReference, XmlElementReference xmlElementReference, XmlElement xmlElement, Predicate`1 propertyFilter)
at Microsoft.Expression.Markup.XamlParser.AddPropertiesAndChildren(XamlParserContext parserContext, DocumentCompositeNodeReference nodeReference, XmlElementReference xmlElementReference, XmlElement xmlElement)
at Microsoft.Expression.Markup.XamlParser.ParseCompositeElement(XamlParserContext parserContext, IDocumentNodeReference nodeReference, IType typeId, XmlElementReference xmlElementReference, XmlElement xmlElement)
at Microsoft.Expression.Markup.XamlParser.ParseElementContent(XamlParserContext parserContext, IDocumentNodeReference nodeReference, IType typeId, XmlElementReference xmlElementReference, XmlElement xmlElement)
at Microsoft.Expression.Markup.XamlParser.ParseElement(XamlParserContext parserContext, IDocumentNodeReference nodeReference, XmlElementReference xmlElementReference, XmlElement xmlElement, DocumentNode& node)
at Microsoft.Expression.Markup.XamlParser.ParseContent(XamlParserContext parserContext, IDocumentNodeReference nodeReference, XmlElementReference xmlElementReference, XmlElement xmlElement, IProperty childProperty, TypeConverter textTypeConverter, ITypeId textType, PropertyHandling propertyHandling)
at Microsoft.Expression.Markup.XamlParser.AddPropertiesAndChildren(XamlParserContext parserContext, DocumentCompositeNodeReference nodeReference, XmlElementReference xmlElementReference, XmlElement xmlElement, Predicate`1 propertyFilter)
at Microsoft.Expression.Markup.XamlParser.AddPropertiesAndChildren(XamlParserContext parserContext, DocumentCompositeNodeReference nodeReference, XmlElementReference xmlElementReference, XmlElement xmlElement)
at Microsoft.Expression.Markup.XamlParser.ParseCompositeElement(XamlParserContext parserContext, IDocumentNodeReference nodeReference, IType typeId, XmlElementReference xmlElementReference, XmlElement xmlElement)
at Microsoft.Expression.Markup.XamlParser.ParseElementContent(XamlParserContext parserContext, IDocumentNodeReference nodeReference, IType typeId, XmlElementReference xmlElementReference, XmlElement xmlElement)
at Microsoft.Expression.Markup.XamlParser.ParseElement(XamlParserContext parserContext, IDocumentNodeReference nodeReference, XmlElementReference xmlElementReference, XmlElement xmlElement, DocumentNode& node)
at Microsoft.Expression.Markup.XamlParser.ParseContent(XamlParserContext parserContext, IDocumentNodeReference nodeReference, XmlElementReference xmlElementReference, XmlElement xmlElement, IProperty childProperty, TypeConverter textTypeConverter, ITypeId textType, PropertyHandling propertyHandling)
at Microsoft.Expression.Markup.XamlParser.AddPropertiesAndChildren(XamlParserContext parserContext, DocumentCompositeNodeReference nodeReference, XmlElementReference xmlElementReference, XmlElement xmlElement, Predicate`1 propertyFilter)
at Microsoft.Expression.Markup.XamlParser.AddPropertiesAndChildren(XamlParserContext parserContext, DocumentCompositeNodeReference nodeReference, XmlElementReference xmlElementReference, XmlElement xmlElement)
at Microsoft.Expression.Markup.XamlParser.ParseCompositeElement(XamlParserContext parserContext, IDocumentNodeReference nodeReference, IType typeId, XmlElementReference xmlElementReference, XmlElement xmlElement)
at Microsoft.Expression.Markup.XamlParser.ParseElementContent(XamlParserContext parserContext, IDocumentNodeReference nodeReference, IType typeId, XmlElementReference xmlElementReference, XmlElement xmlElement)
at Microsoft.Expression.Markup.XamlParser.ParseRootElement(XamlParserContext parserContext, XmlElementReference xmlElementReference, XmlElement xmlElement)
at Microsoft.Expression.Markup.XamlParser.Parse(XamlParserContext parserContext, XmlDocumentReference xmlDocumentReference, XmlDocument xmlDocument)
at Microsoft.Expression.Markup.XamlParser.ParseInternal(XamlParserContext parserContext)
at Microsoft.Expression.Markup.XamlLanguageService.ParseDocument(CancellationToken cancelToken)
at Microsoft.Expression.Markup.MarkupDocument..ctor(IDocumentContext documentContext, ITypeId expectedRootType, ITextBuffer textBuffer, Encoding documentEncoding, IMarkupLanguageService languageService, CancellationToken cancelToken)
at Microsoft.Expression.DesignSurface.Documents.SceneMarkupDocument..ctor(IDocumentContext documentContext, IUndoService undoService, ITypeId expectedRootType, ITextBuffer textBuffer, Encoding documentEncoding, IMarkupLanguageService languageService, CancellationToken cancelToken)
at Microsoft.Expression.DesignSurface.DocumentViewContext.CreateMarkupDocument(ISourceItemContext sourceItem, IHostTextBuffer textBuffer, Encoding encoding, CancellationToken cancelToken)
at Microsoft.Expression.DesignSurface.DocumentViewContext.CreateDocument(ISourceItemContext sourceItem, CancellationToken cancelToken, Boolean isReadOnly, Boolean cloneBufferToStandalone, Boolean suppressUI, SceneDocument originalSceneDocument)
at Microsoft.Expression.DesignSurface.DocumentViewContext.OpenDocument(ISourceItemContext sourceItem, CancellationToken cancelToken, Boolean isReadOnly, Boolean suppressUI)
at Microsoft.Expression.DesignSurface.DesignerService.CreateDesigner(IHostSourceItem item, IHostTextEditor editor, CancellationToken cancelToken)
at Microsoft.Expression.DesignHost.Isolation.Remoting.RemoteDesignerService.<>c__DisplayClass13.<Microsoft.Expression.DesignHost.Isolation.Remoting.IRemoteDesignerService.CreateDesigner>b__12(CancellationToken cancelToken)
at Microsoft.Expression.DesignHost.Isolation.Remoting.RemoteDesignerService.<>c__DisplayClass3`1.<MarshalInWithCancellation>b__2()
at Microsoft.Expression.DesignHost.Isolation.Remoting.STAMarshaler.Call.InvokeWorker()

System.ArgumentException
An item with the same key has already been added.

Server stack trace:
at Microsoft.Expression.DesignHost.Isolation.Remoting.STAMarshaler.WaitForCompletion(NestedCallContext nestedCallContext, BlockingCall call, WaitHandle timeoutSignal)
at Microsoft.Expression.DesignHost.Isolation.Remoting.STAMarshaler.MarshalInSynchronous(Action action, Int32 targetApartmentId, CancellationToken cancelToken, CallModality callModality, String methodName, String filePath, Int32 lineNumber)
at Microsoft.Expression.DesignHost.Isolation.Remoting.STAMarshaler.MarshalIn(Action action, Int32 targetApartmentId, CancellationToken cancelToken, CallSynchronizationMode syncMode, CallModality callModality, String methodName, String filePath, Int32 lineNumber)
at Microsoft.Expression.DesignHost.Isolation.Remoting.ThreadMarshaler.MarshalIn(IRemoteObject targetObject, Action action, CancellationToken cancelToken, CallSynchronizationMode syncMode, CallModality callModality, ApartmentState apartmentState, String memberName, String filePath, Int32 lineNumber)
at Microsoft.Expression.DesignHost.Isolation.Remoting.RemoteDesignerService.MarshalInWithCancellation[TResult](IRemoteCancellationToken remoteToken, Func`2 func, ApartmentState apartmentState)
at Microsoft.Expression.DesignHost.Isolation.Remoting.RemoteDesignerService.Microsoft.Expression.DesignHost.Isolation.Remoting.IRemoteDesignerService.CreateDesigner(IRemoteHostProject remoteProject, 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(IRemoteHostProject remoteProject, IRemoteHostSourceItem remoteItem, IRemoteHostTextEditor remoteEditor, IRemoteCancellationToken cancelToken)
at Microsoft.Expression.DesignHost.Isolation.Remoting.LocalDesignerService.CreateDesignerImpl(IRemoteDesignerService ds, IHostSourceItem item, IHostTextEditor editor, RemoteCancellationToken remoteCancelToken)
at Microsoft.Expression.DesignHost.Isolation.Remoting.LocalDesignerService.<>c__DisplayClass19.<Microsoft.Expression.DesignHost.IDesignerService.CreateDesigner>b__18(IRemoteDesignerService ds, RemoteCancellationToken remoteToken)
at Microsoft.Expression.DesignHost.Isolation.Remoting.LocalDesignerService.<>c__DisplayClass5`1.<MarshalOutWithCancellation>b__4(IRemoteDesignerService ds)
at Microsoft.Expression.DesignHost.Isolation.Remoting.ThreadMarshaler.<>c__DisplayClass1`1.<MarshalOut>b__0()
at Microsoft.Expression.DesignHost.Isolation.Remoting.STAMarshaler.Call.InvokeWorker()

System.ArgumentException
An item with the same key has already been added.
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, CancellationToken cancelToken, String methodName, String filePath, Int32 lineNumber)
at Microsoft.Expression.DesignHost.Isolation.Remoting.STAMarshaler.MarshalOut(Action action, Int32 targetApartmentId, WaitHandle aborted, CancellationToken cancelToken, CallSynchronizationMode syncMode, WaitHandle timeoutSignal, String methodName, String filePath, Int32 lineNumber)
at Microsoft.Expression.DesignHost.Isolation.Remoting.ThreadMarshaler.MarshalOut[TValue](RemoteHandle`1 targetObject, Action action, CancellationToken cancelToken, CallSynchronizationMode syncMode, ApartmentState apartmentState, String methodName, String filePath, Int32 lineNumber)
at Microsoft.Expression.DesignHost.Isolation.Remoting.ThreadMarshaler.MarshalOut[TValue](RemoteHandle`1 targetObject, Action`1 action, CancellationToken cancelToken, CallSynchronizationMode syncMode, ApartmentState apartmentState, String methodName, String filePath, Int32 lineNumber)
at Microsoft.Expression.DesignHost.Isolation.Remoting.LocalDesignerService.MarshalOutWithCancellation[TResult](CancellationToken cancelToken, Func`3 func, ApartmentState apartmentState)
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)