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For some weeks now we have been fighting with an issue where at a small number of customers our Outlook addin gets unloaded and disabled for yet undetermined reasons. By "disabled" I mean that Outlook changes the following registry value from 3 to 2 which in effect means that the addin will not be loaded on next startup: HKEY_LOCAL_MACHINE\Software\Microsoft\Office\Outlook\Addins\[OurAddin.sProgID]\LoadBehavior There is no error message and neither do any exceptions show up in the log files that our addin produces itself. I have already found the following page which specifically deals with the LoadBehavior change issue: http://blogs.msdn.com/vsod/archive/2008/04/22/Troubleshooting-com-add-in-load-failures.aspx However, none of the possible reasons proposed there appear to be applicable: The addin is not merely listed in the Disabled Items list. There are no unhandled exceptions neither in the IDTExtensibility2 methods nor anywhere else in the code. All code is wrapped in try/catch equivalents and all exception output is emitted only via OutputDebugString or into a log file. The error appears to be independent of anti-virus software, i.e. it also occurs with it disabled. Disabling all other addins also has no effect on the error. So, what else can cause Outlook to disable an addin? Some more details / observations: We haven't been able to reproduce the issue in our test environments so far so we haven't yet been able to attach a debugger while the issue occurs. The issue never occurs while we try to watch what happens via remote support (TeamViewer). I suspect this is because TeamViewer uses a hook DLL that injects itself into all running processes (including Outlook) a

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