What do I need to do to develop and deploy a .net dll which exposes COM classes and is registered

Question

I have already developed a .NET assembly which I register to the GAC. This assembly is used by my application and by 4 Office Addins.

I then needed to have a COM interfece for my Office Addins which my Application could also use. I have created a new .dll in .net which exposes COM interfaces. This .dll currently is referenced by my office addins. It is also referenced by the assembly in the GAC.

The problem I have is that I cannot get my office Addins to find the COM dll once deployed on a target machine.

The COM dll is not being added to the GAC it is simply in its own folder within the Application's folder. I am using \codebase and I can see the classes in the registry have a codebase key and they point to the right path.

Fuslogvw confirms it does not work but does not help me any further.

=== Pre-bind state information ===
LOG: DisplayName = MyComConnect, Version=1.0.0.0, Culture=neutral, PublicKeyToken=c0fb9ef9db76b1e7
(Fully-specified)
LOG: Appbase = file:///C:/Program Files (x86)/MyApp/MyAppAddins/MyAppOutlook/
LOG: Initial PrivatePath = NULL
LOG: Dynamic Base = NULL
LOG: Cache Base = NULL
LOG: AppName = OUTLOOK.EXE
Calling assembly : (Unknown).
===
LOG: This bind starts in default load context.
LOG: No application configuration file found.
LOG: Using host configuration file: 
LOG: Using machine configuration file from C:\Windows\Microsoft.NET\Framework\v4.0.30319\config\machine.config.
LOG: GAC Lookup was unsuccessful.
LOG: Attempting download of new URL file:///C:/Program Files (x86)/MyApp/MyAppAddins/MyAppOutlook/MyComConnect.DLL.
LOG: Attempting download of new URL file:///C:/Program Files (x86)/MyApp/MyAppAddins/MyAppOutlook/MyComConnect/MyComConnect.DLL.
LOG: Attempting download of new URL file:///C:/Program Files (x86)/MyApp/MyAppAddins/MyAppOutlook/MyComConnect.EXE.
LOG: Attempting download of new URL file:///C:/Program Files (x86)/MyApp/MyAppAddins/MyAppOutlook/MyComConnect/MyComConnect.EXE.
LOG: All probing URLs attempted and failed.

How or what do I need to do to work out what is going wrong?

A couple of points;

1. On the development machine I have a folder with the COM .dll saved in it and this is what I reference in my projects
2. On build all my projects copy this COM .dll to the bin folder
3. I do not copy the COM .dll with each project in my installation project.
4. In my installation project I have only one folder with the COM .dll in it and register it with \codebase which I thought meant that every project would find it.