c#: Why isn't this ambiguous enum reference resolved using the method signature?

Consider the following code:

namespace ConsoleApplication
{
    using NamespaceOne;
    using NamespaceTwo;

    class Program
    {
        static void Main(string[] args)
        {
            // Compilation error.  MyEnum is an ambiguous reference
            MethodNamespace.MethodClass.Frobble(MyEnum.foo);
        }
    }
}

namespace MethodNamespace
{
    public static class MethodClass
    {
        public static void Frobble(NamespaceOne.MyEnum val)
        {
            System.Console.WriteLine("Frobbled a " + val.ToString());
        }   
    }
}

namespace NamespaceOne
{
    public enum MyEnum
    {
        foo, bar, bat, baz
    }
}

namespace NamespaceTwo
{
    public enum MyEnum
    {
        foo, bar, bat, baz
    }
}

The compiler complains that MyEnum is an ambiguous reference in the call to Frobble(). Since there is no ambiguity in what method is being called, one might expect the compiler to resolve the type reference based on the method signature. Why doesn't it?

Please note that I'm not saying that the compiler should do this. I'm confident that there is a very good reason that it doesn't. I would simply like to know what that reason is.