My VSTO 3.0 Outlook addin doesn't load

Question

I'm trying to diagnose why my Outlook plugin written in C#/VSTO 3.0/VS 2008 doesn't load after being installed.

The plugin works awesomely on my development machine, which has Visual Studio 2008 installed. I can't expect all my users to have all the prerequisites though so I went through these steps to write an installer: http://msdn.microsoft.com/en-us/library/cc563937(loband).aspx

I installed the add-in on a fresh Windows XP SP 2 machine with a fresh install of Outlook 2007. It installs all the prereqs ok (.NET 3.5, VSTO 3.0 runtime, Windows Installer 3.1, 2007 PIAs). Outlook starts but the add-in isn't run. If I go to the Add-ins tab in the Trust Center, I see my add-in in the "Inactive Application Add-ins" section with the message "Not loaded. A runtime error occurred during the loading of the COM Add-in.".

Not sure how to find the specific error so I can fix it.

The reg keys look ok. Under HKEY_CURRENT_USER\Software\Microsoft\Office\Outlook\Addins\BlahAddin I see Description, FriendlyName, LoadBehavior (set to 3 until it fails after which if becomes set to 2), and Manifest.

Tried the VSTO_SUPPRESSDISPLAYALERTS environment variable trick and then launched Outlook from the command line but no output came out.

I have remote debugging more or less working but I'm not sure what to look for. I don't see my DLL loaded when I attach to Outlook, but then again maybe managed DLLs don't show up the same way in VS.

Any other ideas on next steps I could follow to produce a specific error I can diagnose?

Answer 1

Solved my problem after weeks of pain. The "Manifest" reg key was getting corrupted to some junk value during the setup build. It was a known Visual Studio bug that supposedly got fixed in Visual Studio 2008 SP 1, but apparently wasn't for me. Renaming the project name to be different from the plugin name fixed the problem. Random, huh?

Answer 2

Make sure you have try-catch handlers at the top level of all methods called by Outlook and log any exceptions you are unable to handle in some way. Focus your troubleshooting on methods like the Startup method and other methods called during initialization.

Answer 3

You probably want to debug this using the remote debugger. Share out the MSVCMON.EXE folder from your developer machine (in your Visual Studio folders in Program Files) on your test machine (share it with a UNC path), and launch Outlook under the debugger trapping (.NET) exceptions in your modules and putting breakpoints in your methods.

If you need to clean your test computer each time before you install your solution, you should probably run XP under a Virtual PC 2007 VM (free download) and switch to a differencing HD after setting up everything but your plugin to snapshot your pre-installed state once so you don't have to keep uninstalling/reinstalling as you make changes to your program to fix bugs.

Are you installing Debug builds or Release builds? Perhaps one flavor has different requirements. Just guessing.

-Mike [MSFT Office Dev]

Answer 4

On your machine, when you run the addin from Visual Studio, it should create a registry key in HKEY_CURRENT_USER\Software\Microsoft\VSTO\Security\Inclusion{SomeGuid}. Make sure that these registry settings are also being deployed with your addin. They are the ones that allow your code to be trusted.