Error suggests I'm missing a using directive or assembly reference, but I'm not....

I'm pretty new to working with more than one project in a solution. I have two projects: AutoPoster.Droid and AutoPoster.Core.

In AutoPoster.Droid I have an adapter class that references LocationInfo in AutoPoster.Core. I'm now getting this error and not sure why:

The type or namespace 'Core' could not be found (are you missing a using directive or assemblu reference?)

Here is my code:

using System;
using System.Collections.Generic;
using System.Linq;
using Android.App;
using Android.Views;
using Android.Widget;

namespace AutoPoster.Droid.Adapters
{
    public class PostInfoAdapter : BaseAdapter<Core.Model.LocationInfo>
    {
        private readonly Activity activity;
        public List<Core.Model.LocationInfo> LocationInformation { get; private set; } //Getting Error Here
        public PostInfoAdapter(Activity context, IEnumerable<Core.Model.LocationInfo> localInfo)//Getting Error Here
        {
            LocationInformation = new List<Core.Model.LocationInfo>(localInfo);//Getting Error Here
            activity = context;
        }

        public override int Count
        {
            get { return LocationInformation.Count; }
        }

        public override Core.Model.LocationInfo this[int position]//Getting Error Here
        {
            get { return LocationInformation[position]; }
        }

        public override long GetItemId(int position)
        {
            return position;
        }

        public override View GetView(int position, View convertView, ViewGroup parent)
        {
            var view = convertView ?? activity.LayoutInflater.Inflate(Android.Resource.Layout.SimpleListItem2, null);

            var localInfo = LocationInformation[position];

            var name = view.FindViewById<TextView>(Android.Resource.Id.Text1);
            name.Text = !String.IsNullOrEmpty(localInfo.FullName) ? localInfo.FullName : localInfo.ShortName;

            var rxcui = view.FindViewById<TextView>(Android.Resource.Id.Text2);
            rxcui.Text = !String.IsNullOrEmpty(localInfo.FullName) ? localInfo.ShortName : String.Empty;

            return view;
        }

        public void ReloadData(IEnumerable<Core.Model.LocationInfo> locationInformation)//Getting Error Here
        {
            LocationInformation.Clear();
            LocationInformation.AddRange(locationInformation);
            NotifyDataSetChanged();
        }
    }
}