Portable Class Library ICommand compilation error in WPF -- Not sure how to resolve this appropriately?

Some background information: - I am using VS 2013 - I created a Portable Class Library (Targets: .NET 4.5/Silverlight 5/Win Phone 8/Win Store 8) - I implemented the `ICommand` interface in my class named `MyCommand`. MyCommand.cs: ``` public class MyCommand : ICommand { public bool CanExecute(object parameter) { throw new NotImplementedException(); } public void Execute(object parameter) { throw new NotImplementedException(); } public event EventHandler CanExecuteChanged; } ``` I found that when I attempted to reference use the `MyCommand` class in a WPF 4.5 application, I get the following error: The type 'System.Windows.Input.ICommand' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Windows, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e, Retargetable=Yes'. I'm not really sure why this is happening, or what I can do to resolve it appropriately. After scouring the internet, I found answers talking about adding a reference to `System.Windows.dll 4.0.0.0` in my WPF application. Doing this allows me to compile and run the application, but my IDE complains that: Interface member 'void System.Windows.Markup.IComponentConnector.Connect(in, object)' is not implemented. This occurs for my MainWindow.cs class. Is there a better fix than to just deal with this bug so I'm not adding a reference to `System.Windows.dll` in a WPF application which really doesn't need it? And I say that it doesn't really need it because if I copy/paste the `MyCommand` class into the Wpf app it works fine. It only has an issue because I am attempting to use it as a portable class library. UPDATE: It seems that there is more to this than meets the eye. I created a new Wpf Application and used NuGet to reference the MvvmCross solution (since it has an `MvxCommand` object). When I do this, I get the same error. David Kean's answer to a similar question suggests that this should be fixed via VS2012/VS2013 and if not, just reinstall/repair. I fully removed my VS installation and reinstalled it from scratch (VS2013) and still have this issue. So, is this truly a bug or did I do something wrong here? UPDATE 2: I attempted to see if I could assign an instance of the `MyCommand` class to `ICommand`: `ICommand cmd = new MyCommand();` and received the following error: Cannot implicitly convert type 'PortableClassLibrary1.MyCommand' to 'System.Windows.Input.ICommand'. An explicit conversion exists (are you missing a cast?) For some reason the PCL does not seem to type forward the `System.Windows.dll [2.0.5.0]` ICommand to `System.dll [4.0.0.0]` ICommand for my desktop application... Ugh! Update 3: I uploaded my solution so that it is more visible as to what the problem is. Update 4: I've opened a Microsoft connect ticket on this issue. Update 5: After calming down from being upset about this not working... and others telling me that they don't get the same "interface" error. I realize that the "side-effect" of adding `System.Windows.dll` was a ReSharper 8.1 error. I guess it's time to complain to ReSharper instead of Microsoft. sigh