Unity Container ResolutionFailedException when the mapping is correct in the config file

Question

I was using a ServiceLocator which i was DIing with Unity

public ServiceLocator(IUserStore userStore, IProdcutsStore productsStore, ...etc) {}

public IUserStore UserStore 
{ 
    get { return userStore; }
}

This all worked fine, but I wanted lazy instantiation of the repositories as they have quite sparse use.

So my ServiceLocator now looks like

    public ServiceLocator(IUnityContainer container) {}

    public IUserStore UserStore 
    { 
        get { return (IUserStore)container.Resolve(typeof(IUserStore)); }
    }

   //  ...etc

I'm now getting a really unhelpful ResolutionFailedException error

Resolution of the dependency failed, type = "DomainModel.DataServices.Interface.IUserStore", name = "". Exception message is: The current build operation (build key Build Key[DomainModel.DataServices.Interface.IUserStore, null]) failed: The current type, DomainModel.DataServices.Interface.IUserStore, is an interface and cannot be constructed. Are you missing a type mapping? (Strategy type BuildPlanStrategy, index 3)

Telling me my interface type cannot be instantiated because it is an interface is pretty pointless. I know it's an interface you retarded container, that's why you're supposed to be resolving it for me!!

Anyway, the point to note here is that I know the type mapping in the config is fine, as when I was injecting the type interface directly instead of trying to lazy load, it resolved it with no problems.

What am I missing that means something somewhere has to change in order to lazy load this way?

Update: I am guessing what's happening here, is that when I DI the container into the ServiceLocator, the "main" container is instantiating a new container each time which is then not configured properly. I think maybe I need some way to specify that I was to pass this in as the container, rather than resolve it with a new instantiation.