I have a simple class library that I use in Excel. Here is a simplification of my class...

using System;
using System.Runtime.InteropServices;

namespace SimpleLibrary
{
 [ComVisible(true)]
 public interface ISixGenerator
 {
  int Six();
 }

 public class SixGenerator : ISixGenerator
 {
  public int Six() 
  {
   return 6; 
  }
 }
}

In Excel 2007 I would create a macro enabled workbook and add a module with the following code:

Public Function GetSix()
    Dim lib As SimpleLibrary.SixGenerator
    lib = New SimpleLibrary.SixGenerator
    Six = lib.Six
End Function

Then in Excel I could call the function GetSix() and it would return six. This no longer works in Excel 2010 64bit. I get a Run-time error '429': ActiveX component can't create object.

I tried changing the platform target to x64 instead of Any CPU but then my code wouldn't compile unless I unchecked the Register for COM interop option, doing so makes it so my macro enable workbook cannot see SimpleLibrary.dll as it is no longer regsitered.

Any ideas how I can use my library with Excel 2010 64 bit?