Adding Vuforia to an existing Hololens project

I'm trying to add vuforia to an existing hololens project in unity. I get this exception when building the app:

System.TypeInitializationException HResult=0x80131534 Message=The type initializer for 'WinRTBridge.TypeInformation' threw an exception. Source=WinRTBridge StackTrace: at WinRTBridge.TypeInformation..ctor() Inner Exception 1: FileNotFoundException: Could not load file or assembly 'Vuforia.UnityExtensions, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null'. The system cannot find the file specified.

Using Unity 2017.3.1f1 and the built-in Vuforia plugin 7.0.50

When I'm starting the project from the unity player it does work. Also, I've succeeded in deploying the vuforia hololens sample project.

I was able to solve that issue by seeing this thread: https://github.com/Microsoft/MixedRealityToolkit-Unity/issues/1461

apparently there is an issue using vuforia behaviour with the mixed reality camera script.