I've created a test suite in NUnit that references several distinct unit test fixtures in various assemblies.

I've pretty much used the example code from NUnit's docs:

namespace NUnit.Tests
{
    using System;
    using NUnit.Framework;
    using System.Collections;

    public class AllTests
    {
        [Suite]
        public static IEnumerable Suite
        {
            get
            {
                ArrayList suite = new ArrayList();
                suite.Add(new VisionMap.DotNet.Tests.ManagedInteropTest.DotNetUtilsTest());
                return suite;
            }
        }
    }
}

My goal is to add several tests to the list above so I can run them all in a batch.

But when I try to load the DLL in NUnit's GUI I get this:

What am I doing wrong?

I'm using nunit 2.5.0.9122.