Can't Build for web with VR/Cardboard SDK? No key controls?

I am attempting to deploy my VR app developed with Google Cardboard to the web; this game works well in the editor and in iOS however when I build for web all user controls are disabled (the user cannot move or look around using keys or mouse).

I learned from this: http://stackoverflow.com/questions/37152101/unity-cant-move-when-deploying-google-cardboard-vr-app-as-standalone-web/37152187#37152187 that I need to create a new device for Cardboard SDK to support web build. I did this as the link instructed by including

   #elif UNITY_WEBPLAYER
               device = new CardboardWebplayerDevice();

in BaseVRDevice.cs and copying the user controls from UnityEditorDevice.cs into this script. The CardboardWebplayerDevice script is now essentially identical to UnityEditorDevice. When I try to build for web however I get the following errors BRIEFLY then the errors disappear. I'm new to Unity and can't understand why this is happening - how have others built Cardboard VR apps for web?

What am I doing wrong?

Errors: