I've seen tons of posts and sites that address this issue. I've tried every solution I've found but none of them work (I've been trying to figure this out for days now). I have seen many posts with the same exact sounding issue, but either the solution didn't work for me or isn't applicable. With that said...
I have an add-in for Outlook 2007 that is intended to add text to the an email's title and body. It is installed for all users using an .msi file. There is an older version that I deployed last year that works fine. The new version I created has only a few minor input/output changes, nothing major. This new version works perfectly on my development computer in both debug from Visual Studio and from an actual install. However, I can't get it to work on a non-development computer. Here are the details on the program and target computer (development computer and target computer details are the same other than the fact that the target computer doesn't have Visual Studio):
-Using Visual Studio Professional 2013
-Written in Visual Basic
-Target Framework is .NET 4.0
-The add-in is only run once the "send" button on an email is clicked.
-Outlook version is Outlook 2007
-Operating system is Windows 7 Enterprise SP1 32-bit
-Installs fine with no errors.
-HKEY_LOCAL_MACHINE/SOFTWARE/Microsoft/Office/Outlook/Addins/EmailMarkTool/LoadBehavior = 3 after installation.
-VSTO_LOGALERTS = 1
-VSTO_SUPPRESSDISPLAYALERTS = 0
-Outlook opens with no apparent errors.
-LoadBehavior = 0 immediately after Outlook is opened.
-Shows up in the Add-ins under "Inactive Application Add-ins."
-Never shows up under "Disabled Add-ins."
-In the "COM Add-Ins" dialog where I can check which add-ins to use, it shows the correct directory and the Load Behavior is "Unloaded."
-The add-in can be checked. When I click "OK" I don't get any errors. When I go back to the Add-ins, it is unchecked and "Unloaded" again.
-Setting the LoadBehavior to 3 doesn't help because it goes back to 0 as soon as Outlook is started again.
-I inserted a try-catch block into the New() function of the add-in that has a MsgBox pop-up and a Throw.
-I get absolutely no errors anywhere.
-No log file is generated.
I found the problem!
The problem may be unique to Outlook 2007. It turns out Microsoft Office 2007 SP1 and SP2 had a bug that prevented it from running VSTO addins. Microsoft released a hotfix that fixes this issue (https://support.microsoft.com/en-us/kb/976477). This was added in to the release of Microsoft Office SP3. However, to activate the fix, a new registry flag must be created but that isn't automatically done with the fix, making the fix useless until you manually activate it (instructions and download here). So...
To enable VSTO addins in Outlook 2007, you have to add a subkey to this registry:
and add a DWORD "EnableLocalMachineVSTO" with the value set to 1.
I did this, restarted the computer for good measure, installed my addin for the 23rd time, and it installed and ran perfectly! I'm not sure how previous versions worked, though. It's possible that our system admins removed that subkey in an effort to bolster security at some point.