"System.ArgumentException : Cannot compare" when the element is a list

Relevant discussion can be found here. https://groups.google.com/forum/?pli=1#!topic/nunit-discuss/IgGiVyo3fKw

This code throws me a System.ArgumentException : Cannot compare 2 exception.

        public class IntListEqualComparer: IEqualityComparer<List<int>>
        {
            public bool Equals(List<int> x, List<int> y)
            {
                return x.Count == y.Count;
            }

            public int GetHashCode(List<int> obj)
            {
                return obj.Count.GetHashCode();
            }
        }

        [Test]
        public void IntListListTest()
        {
            var list1 = new List<int>() {2, 3};
            var list2 = new List<int>() {2, 3};

            var list11 = new List<List<int>>() {list1};
            var list22 = new List<List<int>>() { list2 };
            var comparer = new IntListEqualComparer();
            Assert.That(list11, new CollectionEquivalentConstraint(list22).Using(comparer));
        }

It seems that Nunit can't compare if the elements are of the type List?

Here's the complete stack trace:

failed: System.ArgumentException : Cannot compare 2
 at NUnit.Framework.Constraints.EqualityAdapter.EqualityComparerAdapter`1.ObjectsEqual(Object x, Object y)
 at NUnit.Framework.Constraints.NUnitEqualityComparer.ObjectsEqual(Object x, Object y)
 at NUnit.Framework.Constraints.NUnitEqualityComparer.CollectionsEqual(ICollection x, ICollection y)
 at NUnit.Framework.Constraints.NUnitEqualityComparer.ObjectsEqual(Object x, Object y)
 at NUnit.Framework.Constraints.CollectionItemsEqualConstraint.CollectionTally.ItemsEqual(Object expected, Object actual)
 at NUnit.Framework.Constraints.CollectionItemsEqualConstraint.CollectionTally.TryRemove(Object o)
 at NUnit.Framework.Constraints.CollectionItemsEqualConstraint.CollectionTally.TryRemove(IEnumerable c)
 at NUnit.Framework.Constraints.CollectionEquivalentConstraint.doMatch(IEnumerable actual)
 at NUnit.Framework.Constraints.CollectionConstraint.Matches(Object actual)