Cannot find "VuforiaMonoBehavior" with Sample Scenes 7.1.31 + Unity 2017.3.1p1

Hello,

I am currently trying to build the Mars Rover Model Target sample scene (from here: https://developer.vuforia.com/downloads/beta). I followed the set up instructions here: https://library.vuforia.com/articles/Training/Developing-Vuforia-Apps-for-HoloLens

However, when I try to press play in Unity or build the project, I get the following errors:

"Assets/Vuforia/Scripts/DefaultInitializationErrorHandler.cs(18,50): error CS0246: The type or namespace name `VuforiaMonoBehaviour' could not be found. Are you missing an assembly reference?"

"Assertion failed: Assertion failed on expression: 'm_CurrentEntriesPtr != NULL && m_IsGettingEntries'

UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)"

I am using the Sample Scenes 7.1.31, Unity 2017.3.1p1, and Visual Studio 2015 version 14.0.

Steps I've tried to resolve this:

I'm not sure why this class is missing. On another app, when I encountered this problem, I changed VuforiaMonoBehavior to just "MonoBehavior". When I pressed play, I received another error "Assets/Vuforia/Scripts/DefaultTrackableEventHandler.cs(61,57): error CS0117: `Vuforia.TrackableBehaviour.Status' does not contain a definition for `NO_POSE'. Changing NO_POSE to "NOT_FOUND" resolved this error, but I am confused about why this is as NOT_FOUND is deprecated (https://library.vuforia.com/content/vuforia-library/en/reference/unity/classVuforia_1_1TrackableBehaviour.html). This allowed me to play from unity (sometimes), but I got nullreference exceptions and overall performance of the app was very buggy and unstable.

It seems to me like I am missing some kind of update, but I'm not sure what. Any insight would be greatly appreciated!