Vuforia Unity 2018.2 not working on Android

Hi! I hope you can help me figuring out how to solve this issue..

I am delivering support for a game that is using Vuforia. To make it work with current Play Store requirements, we are using Unity 2018.2.2. 

I cannot find a Vuforia version number, but the source code says Copyright 2010 - 2014. 

The game has a Vuforia AR scene. This runs fine in the editor, and uses the computer webcam as a camera. However, when building to android, the screen is black. In the Debugger we see an OPENGL NATIVE PLUG-IN ERROR. Here is the output of the log. 

<i>AndroidPlayer(LENOVO_Lenovo_TB-X304F@192.168.1.3)</i> Vuforia initialization successful // some other Vuforia Tracker initialisation <i>AndroidPlayer(LENOVO_Lenovo_TB-X304F@192.168.1.3)</i> StartVuforia

<i>AndroidPlayer(LENOVO_Lenovo_TB-X304F@192.168.1.3)</i> Assertion failed: OPENGL NATIVE PLUG-IN ERROR: GL_INVALID_FRAMEBUFFER_OPERATION: Framebuffer is not complete or incompatible with command UnityEngine.GL:IssuePluginEvent(Int32) Vuforia.VuforiaRendererImpl:UnityRenderEvent(RenderEvent) Vuforia.VuforiaManagerImpl:StartRendering() Vuforia.VideoBackgroundAbstractBehaviour:RenderOnUpdate() Vuforia.VuforiaAbstractBehaviour:UpdateStatePrivate(Boolean, Boolean) Vuforia.VuforiaAbstractBehaviour:Update()

the error is thrown every frame. 

I have tried all the solutions that were suggested on this forum, but none we're working.

Can you tell me how to solve this error in  Vuforia 2014 to get it working on Android? Or is there an incompatibility between Vuforia 2014 and Unity 2018?

Is it possible to upgrade Vuforia 2014 to Vuforia 8 while keeping the existing trackers working? We do not have access to the original developer trackers, so the upgrade would need to be done while retaining the existing trackers. 

Many thanks for helping out!