StructureMap web.config

Question

I have this interface

public interface ICartService : IService<Cart>
    {
        ...
    }

Implementation of the interface

public class CartService : ICartService
    {
        public CartService(ICartRepository repository)
        {
            _repository = repository;
        } 
...
}

And in web.config

  <StructureMap MementoStyle="Attribute">
    <DefaultInstance Key="CartService" PluginType="xxxx.Catalog.Services.ICartService,xxxx.Catalog" PluggedType="xxxx.Catalog.Services.Default.CartService,xxxx.Catalog" Scope="Singleton"  />    
  </StructureMap>

of course I called on app start:

 ObjectFactory.Initialize(y =>
            {
                y.PullConfigurationFromAppConfig = true;
});

and getting error No Default Instance defined for PluginFamily xxxx.Catalog.Services.ICartService, xxxx.Catalog

Any ideas what am I doing wrong?