Deploying COM Add-ins for 64-bit Office using Visual Studio (Saaid Khan for Nathan Halstead)

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Nathan Halstead is a Program Manager on the Visual Studio Team. He is responsible for various aspects of Visual Studio extensibility, and is an avid ice hockey enthusiast. On occasion, he’s been known to guest author technical articles on various Microsoft blogs and forums. My only contribution to this blog is posting it here :). Here is what Nathan has to say:

Later this year, Microsoft will release the next version of its Office productivity suite – Office 2010. The 2010 release will be offered in both 32 and 64-bit flavors. The new 64-bit flavor of Office is especially useful for enabling computationally rich applications requiring larger amounts of system resources. However, the move to 64-bit poses some additional challenges for add-in developers who want to target both the 32 and 64-bit versions of Office.

For the past few releases, Visual Studio has shipped with several templates for creating add-ins for Office. If you are planning to build extensions for Office, and have not already done so, I strongly encourage you to take a look at the Visual Studio Tools for Office (VSTO) templates, which offer visual designers and managed APIs for developing and testing your Microsoft Office extensions.

If you can’t or don’t want to use the VSTO templates, Visual Studio also offers a bare-bones template for developing COM-based add-ins for Office called the “Shared Add-in” template. This template generates a solution which includes a basic implementation Office’s IDTExtensibility2 interface, and a lightweight MSI project for deploying the add-in. For the past several years, this bare-bones template has been sufficient for getting started with Office extensibility. If, however, you want to use it to target 64-bit Office, there are a few issues you might encounter that you should be aware of. This article will briefly walk you through these issues and explain how to work around them.

Creating a new Shared Add-in

To create a new Shared Add-in, select the project template from the new project dialog. For the purposes of this example, we will be creating a globally registered C# based add-in using Visual Studio 2008. To do this, launch Visual Studio with Administrator privileges (to ensure the build process has permissions to the HKCR registry hive) and select a new Shared Add-in under “Other Project Types -> Extensibility”:


A wizard will appear to guide you through the creation of your Add-in. Note that if you did not launch Visual Studio with Administrator privileges, the option to globally register your add-in will be disabled:


When you’ve finished the wizard, your solution will be generated, and configured for proper x86 deployment.

Registering the add-in with 64-bit Office for debugging

When the Shared Add-In Wizard finishes generating the solution, it automatically registers your add-in with the Office applications specified in the wizard. This ensures that debugging can work without running your setup application. If you selected the “My add-in should be available to all users…” option in the wizard, it registers your add-in to the 32-bit global registry location viewable in Regedit as [HKLM\Software\Wow6432Node\Microsoft\Office\<App>\AddIns\<AddInName>].

However, 64-bit Office cannot see registration information in this location. To load your add-in automatically, this registration information will need to be copied to 64 bit registry locations for 64-bit Office to see. To do this, copy all of the registry keys under [HKLM\Software\Wow6432Node\Microsoft\Office\<App>\AddIns\<AddInName>] to [HKLM\Software\Microsoft\Office\<App>\AddIns\<AddInName>].

For example, you would copy the following keys for Word registration:













Retargeting for x64 deployment


With your new solution in hand, the next step is to update its installer to follow 64-bit Windows deployment conventions. To do this, select the Setup project in the Solution Explorer, and update the project’s TargetPlatform property to x64 in the Properties window.

If you are using Visual Studio 2010, this is the only change that should be needed for your deployment project. Your installer will now be able to properly register your add-in with 64-bit versions of Office!

However, if you are using Visual Studio 2008, a bug in the deployment project system prevents the proper registration of 64-bit COM components. To work around this limitation, follow the instructions listed in the listed in the Troubleshooting Windows Installer Deployments topic on MSDN. See the Cannot load 64-bit self-registering DLL’s section, which describes in detail how to work around this for your Shared-Add-in assemblies by manually writing the 64-bit registry keys that register your COM assemblies.

Making your entire solution 64-bit

While native C++ applications will need to be updated to explicitly target 64-bit machines, in most cases Office will happily load your.NET add-ins without requiring you to explicitly target an x64 platform. However, there are situations where you will have to update your .NET assembly to be explicitly 64-bit. For example, Misha Shneerson highlights a situation on his blog where you may choose to use unsafe code to preserve icon transparency when rendering Office icons. If you use unsafe code, then you will need to recompile your assembly for the x64 platform.

Before doing this, you should familiarize yourself with some of the work that may be involved to ensure your add-in works properly when running 64-bit. There are a large number of resources available on this topic, but this MSDN article does a good job covering some of the fundamental considerations for .NET applications, and this vintage MSDN Magazine article does a fantastic job for native C++ applications.

If you need to build a 64-bit assembly, you will need to update your project’s build properties to do so. You may do this from within the properties editor for your project. For example, in a C# project, right click, and select properties to open the properties editor:


Navigate to the build tab, and change the Platform Target to x64:


For most Visual Studio projects, a 64-bit binary would be generated when you save and build. However, there is a bug in the VB and C# project systems that causes a build error for Shared Add-in projects. When you attempt to build, you will receive an error that states that your dll “is not a valid assembly.”

The culprit is the “Register for COM interop” project setting on the build tab:


By selecting this checkbox, a build task is automatically generated to register the COM assembly. This is used by the template to make it easier to test your add-in by automatically deploying your assembly on your machine. However, this task uses the 32-bit version of the regasm tool, which throws a “is not a valid assembly” error when run against 64-bit assemblies. The workaround for this issue is described in KB Article 956933, and involves unchecking this option, and creating your own build event to do the 64-bit registration.

A best practice for COM add-ins

With your setup project and your add-in assemblies updated, you will now be able to install and run your COM addin inside 64-bit Office applications! However, if you decide to build your add-in for Office without using VSTO, I would highly recommend using the COM Shim wizard, which will help you isolate your add-in ino a separate app-domain for better resiliency:

· VS 2008 COM Shim Wizard

· VS 2010 COM Shim wizard

· COM Shims and x64 Office


If you have additional recommendations and best-practices you think would be helpful to share, please include these in the comments! Have fun extending Office 2010!

Saaid Khan, Program Manager

  • Hi,

    I am facing one problem with VSTO add-ins on Windows 2008 server R2 64 bit machine. We want to make the addin available to all users. We found hotfix kb976477 and now our com-addin are available for other users too. However it is giving big problem after installing the hotfix add-in menu is not at all visible on menu bar. We selected the com add-in from excel option- add-in - manage - com addin and selected the add-ins.

    Can you please let us know why the add-in menu disappeared?



  • hi, admin

    thanks for your share, very useful

  • A best practice for COM add-ins very useful

  • Hi,

       I  created a shared addin with VS2010, 64-bit Office 2010. The shared addin was created with C++ language. The addin can be load and run in the machine created it. I  copy the whole project to the other machine, it can' t load in other machine.And  when I  rebuild the project in other machine, it can load and run successful.

        I  see your sentence"With your setup project and your add-in assemblies updated", I want to know how to update the add-in assemblies?

  • Hi,

       I  created a shared addin with VS2010, 64-bit Office 2010. The shared addin was created with C++ language. The addin can be load and run in the machine created it. I  copy the whole project to the other machine, it can' t load in other machine.And  when I  rebuild the project in other machine, it can load and run successful.

        I  see your sentence"With your setup project and your add-in assemblies updated", I want to know how to update the add-in assemblies?

  •      I  created a shared addin with VS2008 (OS is WinXP 32bit ), and Want to run in Win7 64-bit Office 2007(VM). My develop PC don't has the path   "[HKLM\Software\Wow6432Node\ ..." , How can I do your step?

    " copy the following keys for Word registration"??

  • How to copy the "HKLM\Software\Wow6432Node\Microsoft..." HKLM\Software\Microsoft", I tried the steps. Nothing works.

  • I have created vsto addins for word and powerpoint using vs2010. Now i want to create a single setup for both 32 bit and 64 bit machine. Is it possible? if yes, then how it will be created. And how the setup will run according to machine type i.e.  32 bit and 64 bit.

  • OMG!  I have just spent almost a whole day on getting a 32 bit based object to compile in 64 W& with VS2008.  The reference to  KB Article 956933 was all I needed.

    Thank you.

  • I create an COM add-in. It  normal runs at excel  x86,but it throws exception at excel 2010 x64.

    what cause the issues?

    How to solve the issues?

  • Hey any body that can help me on how to develop an add-in code in C# that validates ms project plans.Thanks!!

  • Hi,

    I'm using VS2013, office 2013 64bit, oracle express edition 10g 32bit.

    whenever I connect my project to oracle and I want to debug it, I would face with the following error:

    "attempt to load oracle client libraries threw badimageformatexception. this problem will occur when running in 64bit mode with 32bit oracle client components installed"

    would you please assist me in this regard?

    Best Regards

    Hadi Pouyanfard

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Deploying COM Add-ins for 64-bit Office using Visual Studio (Saaid Khan for Nathan Halstead)