An item with the same key has already been added when creating new WPF project

Question

I just created a new WPF project in Visual Studio 2015 Pro, and after the Creating Project dialog disappears, I do not get the designer. This ArgumentException just shows there and I have not added any controls or anything. Just created the project and I get this.

I have read this exception is thrown when I have duplicate files like a resx file with Resources.resx name or LIKE when I am using the same file twice but I am not doing anything else than creating a new project.

I can build the solution and the project successfully with no errors. I open the compiled EXE and it looks OK. But I cannot use the designer inside VS.

This WPF solution targets .NET4.5. I tried creating a new one targetting other .NET versions but the same happens.

[EDIT] Here is the entire exception thrown by VS:

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 System.Collections.Generic.Dictionary`2.Add(TKey key, TValue value)
   at Microsoft.VisualStudio.DesignTools.Utility.Telemetry.VsTelemetryService.RegisterDesignerProcessSession(Int32 pid)
   at Microsoft.VisualStudio.DesignTools.Utility.Feedback.WatsonTracker.RegisterSession(Int32 processID)
   at Microsoft.VisualStudio.DesignTools.Utility.DesignerSessionTracker.RecordDesignerStart(Int32 processID, String isolationTargetIdentifier, Boolean mockCustomTypes, String buildConfiguration)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Primitives.ProcessDomainFactory.ProcessIsolationDomain..ctor(ProcessDomainFactory factory, IIsolationBoundary boundary, AppDomainSetup appDomainInfo, IIsolationTarget isolationTarget, String baseDirectory)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Primitives.ProcessDomainFactory.CreateIsolationDomain(IIsolationBoundary boundary)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Primitives.IsolationBoundary.Initialize()
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.Primitives.IsolationBoundary.CreateInstance[T](Type type)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.IsolatedObjectFactory.Initialize()
   at Microsoft.VisualStudio.DesignTools.DesignerHost.Services.VSIsolationService.CreateObjectFactory(IIsolationTarget isolationTarget, IObjectCatalog catalog)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.IsolationService.CreateLease(IIsolationTarget isolationTarget)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.IsolatedDesignerService.CreateLease(IIsolationTarget isolationTarget, CancellationToken cancelToken, DesignerServiceEntry& entry, IServiceProvider serviceOverrides)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.IsolatedDesignerService.IsolatedDesignerView.CreateDesignerViewInfo(CancellationToken cancelToken)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.IsolatedTaskScheduler.InvokeWithCulture[T](CultureInfo culture, Func`2 func, CancellationToken cancelToken)
   at Microsoft.VisualStudio.DesignTools.DesignerContract.Isolation.IsolatedTaskScheduler.<>c__DisplayClass10_0`1.<StartTask>b__0()
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.Tasks.Task.Execute()

Here is a screenshot too:

Hope someone can help me solve this problem. Thanks in Advance - CCB

Answer 1

I got the same exception and reduced both xaml and cs to a minimum without any help. I deleted folders bin and obj, restarted VS, rebooted my computer, but still no luck. With VS 2012 the designer was not loading with a different error message. This post helped me fix the issue

FIX: Delete or rename file "C:\Program" then click on "Click here to reload the designer".

In my case Program was a text file without extension from writing the output of an ipconfig MS-DOS command. There is no need to close the xaml designer, recompile, clear the cache, or restart Visual Studio.

Somehow VS tries to read it when loading the designer (checked with Process Monitor from Sysinternals). For information the stack in Visual Studio 2012 was the same as this bug report.

System.Runtime.Remoting.RemotingException
[] Designer process terminated unexpectedly!
   at Microsoft.Expression.DesignHost.Isolation.Primitives.ProcessDomainFactory.ProcessIsolationDomain.Microsoft.Expression.DesignHost.Isolation.IIsolationDomain.CreateInstance(String assemblyName, String assemblyCodeBase, String typeName)
   at Microsoft.Expression.DesignHost.Isolation.Primitives.IsolationBoundary.Initialize()
   at Microsoft.Expression.DesignHost.Isolation.Primitives.IsolationBoundary.CreateInstance[T](Type type)
   at Microsoft.Expression.DesignHost.Isolation.IsolatedExportProvider.Initialize()
   at Microsoft.VisualStudio.ExpressionHost.Services.VSIsolationService.CreateExportProvider(IIsolationTarget isolationTarget, ICatalogFactory catalogFactory, IExportFilter filter)
   at Microsoft.Expression.DesignHost.Isolation.IsolationService.CreateLease(IIsolationTarget isolationTarget)
   at Microsoft.Expression.DesignHost.IsolatedDesignerService.CreateLease(IIsolationTarget isolationTarget, CancellationToken cancelToken, DesignerServiceEntry& entry)
   at Microsoft.Expression.DesignHost.IsolatedDesignerService.IsolatedDesignerView.CreateDesignerViewInfo(CancellationToken cancelToken)
   at Microsoft.Expression.DesignHost.Isolation.IsolatedTaskScheduler.InvokeWithCulture[T](CultureInfo culture, Func`2 func, CancellationToken cancelToken)
   at Microsoft.Expression.DesignHost.Isolation.IsolatedTaskScheduler.<>c__DisplayClassa`1.<StartTask>b__6()
   at System.Threading.Tasks.Task`1.InnerInvoke()
   at System.Threading.Tasks.Task.Execute()