If you try to install VirtualKD 2.8 on VirtualBox 4.2.x, you get an error similar to this:

Unable to cast COM object of type ‘VirtualBox.VirtualBoxClass’ to interface type ‘VirtualBox.IVirtualBox’. This operation failed because the QueryInterface call on the COM component for the interface with IID ‘{…}’ failed due to the following error: No such interface supported (Exception from HRESULT: 0x80004002 (E_NOINTERFACE)).

It turns out it’s a pretty easy thing to fix. The Interop.VirtualBox.dll distributed with VirtualKD is built for the 4.1 VirtualBox interface, so you just have to rebuild it for your version of VirtualBox. Create a C# project, and paste the following code into the Program.cs file to build a new Interop.VirtualBox.dll for 4.2.x.

using System;
using System.Reflection;
using System.Reflection.Emit;
using System.Runtime.InteropServices;

namespace ConvertTypeLibToAssembly
{
    public class App
    {
        private enum RegKind
        {
            RegKind_Default = 0,
            RegKind_Register = 1,
            RegKind_None = 2
        }
    
        [ DllImport( "oleaut32.dll", CharSet = CharSet.Unicode, PreserveSig = false )]
        private static extern void LoadTypeLibEx( String strTypeLibName, RegKind regKind, 
            [ MarshalAs( UnmanagedType.Interface )] out Object typeLib );
        
        public static void Main()
        {
            Object typeLib;
            LoadTypeLibEx( @"C:\Program Files\Oracle\VirtualBox\VBoxC.dll", RegKind.RegKind_None, out typeLib ); 
            
            if( typeLib == null )
            {
                Console.WriteLine( "LoadTypeLibEx failed." );
                return;
            }
                
            TypeLibConverter converter = new TypeLibConverter();
            ConversionEventHandler eventHandler = new ConversionEventHandler();
            //AssemblyBuilder asm = converter.ConvertTypeLibToAssembly( typeLib, "Interop.Virtualbox.dll", 0, eventHandler, null, null, null, null );
            AssemblyBuilder asm = converter.ConvertTypeLibToAssembly(typeLib, "Interop.VirtualBox.dll", TypeLibImporterFlags.SafeArrayAsSystemArray, eventHandler, null, null, "VirtualBox", null); //using assembly name "VirtualBox" and SafeArrayAsSystemArray to be compatible to VisualStudio-Generated Interop-Assembly

            asm.Save("Interop.Virtualbox.dll");
        }
    }

    public class ConversionEventHandler : ITypeLibImporterNotifySink
    {
        public void ReportEvent( ImporterEventKind eventKind, int eventCode, string eventMsg )
        {
            // handle warning event here...
        }
        
        public Assembly ResolveRef( object typeLib )
        {
            // resolve reference here and return a correct assembly...
            return null; 
        }    
    }
}

Some of this code was grabbed from MSDN, and a single line was grabbed from VirtualBoxService. As the latter is GPL, this code may be GPL. I don’t claim any rights to it.