Caliburn.Micro ViewModel and ActivateItem - does not exist in the current context

The following code was working until I updated to the latest copy of Caliburn. Now I get an error on ActivateItem where it indicates it does not exist in the current context. Any suggestions?

using Caliburn.Micro;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace JCWPFUserInterface.ViewModels
{
    public class ShellViewModel : Conductor<object>
    {
        LoginViewModel _loginVM;
        public ShellViewModel(LoginViewModel LoginVM)
        {
            _loginVM = LoginVM;
            ActivateItem(_loginVM);
        }
    }
}