Registering x64 Assemblies for COM Interop

Question

Scenario: I have a project containgin two C# projects, which for historical reasons must communicate with each other using COM (via COM Interop). The COM Server is an in-process automation object (call this the "Server") and the COM Client is a simple C# Console application that loads the server like this:

        var objTypee = Type.GetTypeFromProgID("ProgID.Interop3264");
        var objLateBound = Activator.CreateInstance(objType);

Visual studio automatically registers assemblies for COM Interop if that option is enabled in the project settings, so that's what I use to register the Server (I'm only interested in the developer experience here, installation is a seperate issue) and everything works fine as long as the projects are set to generate 32-bit code or the COM Client is 32-bit.

The problem comes when developing on a 64-bit system and both projects are set to generate code for 'Any CPU' which results in them running in 64-bit mode. This yields the following error:

"Retrieving the COM class factory for component with CLSID {6F597EDF-9CC8-4D81-B42E-1EA9B983AB02} failed due to the following error: 80040154."

After some investigation, it seems that the MSBuild scripts only perform 32-bit registration. It does put the ProgID into the 64-bit registry section, along with its subkey CLSID, and the proper classID. But the CLSID{clsid} stuff is not there. It's only in the WOW6432 subtree, for 32-bit. So the activator cannot retrieve the class factory because it can't find the thing.

I'll be really impressed with the SO community if I get an answer to this one, but here goes:

Has anyone else run accross this problem? How did you solve it? What's the easiest way to ensure that COM Interop assemblies get correctly registered on 64-bit development machines?

Answer 1

We've encountered this problem and solved it by setting projects up to generate assemblies for x86. This is suboptimal, of course, but we also have several native 32-bit libs, so we had to do that anyway.

Answer 2

I was able to solve this with the following KB item. Basically I turned off registering for COM interop in the project build settings, and used the post-build command:

"%Windir%\Microsoft.NET\Framework64\v2.0.50727\regasm" "$(TargetPath)" 

http://support.microsoft.com/kb/956933