Building to Windows Store (Windows Phone 8.1)

I'm trying to deploy my game to my Windows Phone (8.1). I've registered it and got a temporary license but I keep getting this error:

Exception: Failed to build Visual Studio project. Output: C:\Users\Alexander\Documents\Whale, Whale Executable\Whale, Whale\Whale, Whale.csproj(177,3): error MSB4019: The imported project "C:\Program Files (x86)\MSBuild\Microsoft\WindowsXaml\v12.0\Microsoft.Windows.UI.Xaml.CSharp.targets" was not found. Confirm that the path in the declaration is correct, and that the file exists on disk.

UnityEditor.WP8.BuildPostprocessor.Build (System.String installPath, System.String packageName, System.String configuration, System.String platform) (at C:/buildslave/unity/build/PlatformDependent/WP8Player/Extensions/Managed/ExtensionModule.cs:174) UnityEditor.WP8.BuildPostprocessor.LaunchPlayer (BuildLaunchPlayerArgs args) (at C:/buildslave/unity/build/PlatformDependent/WP8Player/Extensions/Managed/ExtensionModule.cs:62) UnityEditor.PostprocessBuildPlayer.Launch (BuildTarget target, System.String path, System.String productName, BuildOptions options) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/PostprocessBuildPlayer.cs:282)

Any idea on how to fix it?