I'm testing with a VB6 client (no 'Controls.Add') and really I don't want any
of that VB code at all - all I want is the UserControl on the form and a
"UserControl11_DoStuff()" event handler, just like a button has its Click()
handler.

At design time, when I double-click the UserControl on the form then VB
creates the DoStuff() handler, but at run-time it never gets called.

Yes, I've got that explicit IDispatch interface declared for the user
control's event. Still no luck though!
Here is the entire code for the C# control (which has only a button on it!):

namespace WinControl1
{
    [ComVisible(false)]
    public delegate void TestEventDelegate();

    [Guid("C9CCDB9B-5A41-44b7-A54E-6D6DE0826EF5")]
    [InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
    [ComVisible(true)]
    public interface IUserControl1
    {
        [DispId(1)]
        void Test();
    }

    [Guid("DCFF96F9-9F3B-4576-A144-E4CD030614B0")]
    [InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
    [ComVisible(true)]
    public interface IUserControl1Events
    {
        [DispId(1)]
        void TestEvent();
    }

    [Guid("F4A79199-9FA1-4810-AE34-F1EAC0437980")]
    [ComVisible(true)]
    [ClassInterface(ClassInterfaceType.None)]
    [ComSourceInterfacesAttribute(typeof(IUserControl1Events))]
    public partial class UserControl1 : UserControl, IUserControl1
    {
        public event TestEventDelegate TestEvent;

        public UserControl1()
        {
            InitializeComponent();
        }

        public void button1_Click(object sender, EventArgs e)
        {
            MessageBox.Show(".net control: Button Press");
            if (TestEvent == null)
                MessageBox.Show("TestEvent delegate is null");
            else
                TestEvent();
        }
       
        public void Test()
        {
            MessageBox.Show("Test method called");
            if (TestEvent != null)
                TestEvent();
        }
       
        [ComRegisterFunction]
        static void ComRegister(Type t)
        {
            string keyName = @"CLSID\" + t.GUID.ToString("B");
            using (RegistryKey key =
                    Registry.ClassesRoot.OpenSubKey(keyName, true))
            {
                key.CreateSubKey("Control").Close();
                using (RegistryKey subkey = key.CreateSubKey("MiscStatus"))
                {
                    subkey.SetValue("", "131457");
                }
                using (RegistryKey subkey = key.CreateSubKey("TypeLib"))
                {
                    Guid libid = Marshal.GetTypeLibGuidForAssembly(t.Assembly);
                    subkey.SetValue("", libid.ToString("B"));
                }
                using (RegistryKey subkey = key.CreateSubKey("Version"))
                {
                    Version ver = t.Assembly.GetName().Version;
                    string version =
                     string.Format("{0}.{1}",
                                    ver.Major,
                                    ver.Minor);
                    if (version == "0.0") version = "1.0";
                    subkey.SetValue("", version);
                }
            }
        }

        [ComUnregisterFunction]
        static void ComUnregister(Type t)
        {
            // Delete entire CLSID\{clsid} subtree
            string keyName = @"CLSID\" + t.GUID.ToString("B");
            Registry.ClassesRoot.DeleteSubKeyTree(keyName);
        }
       
    }
}

My understanding was that this applies only to .net framework 1 and that
support had improved for version 2.0. The KB article says it only applies to
.net framework 1.0 and 1.1.

This whole subject area does seem somewhat vague in the MS documentation!

Hi Peter,

To be honest, I'm not particularly worried about VB6 support. I was using
VB6 simply as a test bed.

What I am aiming for is getting a WinForm into an existing MFC6 application.
I've seen that it's possible to get a WinForm control into an MFC8 app but I
was hoping to avoid migrating the MFC6 app to MFC8. Hence me thinking down
the route of wrapping the WinForm control in ActiveX. (I was initially hoping
for embedding a WinForms "Form" and having it appear as an MDI child rather
than a WinForm control but this seems a non-starter).

Cheers,
Aled.