The integration for Ogre3D has been made only for Coherent UI 1.x. The error is due to UISystem not being used in Coherent 2.x. ViewContext in Coherent Browser 2.x is the equivalent of Coherent UI 1.x’s UISystem. The changes needed for the integration are not excessive. We are open to pull request, so if you decide to update it we would be happy to verify and integrate your changes.
I will compile a guide with the changes between Coherent UI 1.x and 2.x and will attach it to this post when ready.
Edit: Here is the guide that contains more information related to the API changes and general 1.x -> 2.x migration.