title: Windows Phone 8.1 build fails on Unity 5.2.3f1
body: <p>I am trying to publish our games on the Windows 8.1 store but I keep getting this error:</p>
  
  <p>========</p>
  
  <blockquote>
    <p>UnityException: Platform assembly not found.
    Make sure Visual Studio 2013 and Windows Phone SDK 8.1 is installed.
    PostProcessWinRT.CheckSDK () (at C:/buildslave/unity/build/PlatformDependent/WinRT/SharedSources/CSharp/PostProcessWinRT.cs:164)
    PostProcessWinRT.Process () (at C:/buildslave/unity/build/PlatformDependent/WinRT/SharedSources/CSharp/PostProcessWinRT.cs:103)
    UnityEditor.Metro.BuildPostprocessor.PostProcess (BuildPostProcessArgs args) (at C:/buildslave/unity/build/PlatformDependent/MetroPlayer/Extensions/Managed/ExtensionModule.cs:99)
    UnityEditor.PostprocessBuildPlayer.Postprocess (BuildTarget target, System.String installPath, System.String companyName, System.String productName, Int32 width, Int32 height, System.String downloadWebplayerUrl, System.String manualDownloadWebplayerUrl, BuildOptions options, UnityEditor.RuntimeClassRegistry usedClassRegistry) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/PostprocessBuildPlayer.cs:316)
    UnityEditor.HostView:OnGUI()</p>
  </blockquote>
  
  <p>========</p>
  
  <p>I have a fresh install of Windows 8.1 Enterprise. Fresh download of Unity 5.2.3f1 with the standard installer of visual studio community 2015. All windows updates applied and no other software installed on the machine. I am trying this with a fresh project.</p>