Compiler error when not including the parameter types from another constructor

I'm using C# under VS2012 v.11.0.61030.00 Update 4. I have a class with two constructors: one for normal use, and one that injects a dependency for the purposes of unit testing.

using ServiceLayer;

namespace PresentationLayer
{
    public class Orchestrator
    {
        private NumberService svc;

        public Orchestrator(int i)
        {
            svc = new NumberService(i);
        }

        public Orchestrator(NumberService providedService)
        {
            svc = providedService;
        }

        public int Get()
        {
            return svc.GetInt();
        }
    }
}

The "NumberService" is in a second project:

namespace ServiceLayer
{
    public class NumberService
    {
        private int x;

        public NumberService(int i)
        {
            x = i;
        }

        public int GetInt()
        {
            return x;
        }
    }
}

The PresentationLayer project is in turn referenced by the app (in this case, a console app):

using System;
using PresentationLayer;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Orchestrator o = new Orchestrator(8);
            Console.WriteLine(o.Get());
        }
    }
}

The line Orchestrator o = new Orchestrator(8); throws a compiler error as follows:

The type 'ServiceLayer.NumberService' is defined in an assembly that is not referenced. You must add a reference to assembly 'ServiceLayer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.

This appears to be because VS cannot differentiate between the two constructors without knowing what a NumberService is. However, if I change the number of parameters...

public Orchestrator(int i, bool b)
{
    svc = new NumberService(i);
}

and

static void Main(string[] args)
{
    Orchestrator o = new Orchestrator(8, true);
    Console.WriteLine(o.Get());
}

Suddenly it's quite happy to compile. I feel that one of these two behaviors is in error: either it's okay not to know what a given class is, or it's not. Does anyone have a better explanation or fix for this?