When I use the Add... button from the COM add-ins list to add my DLL,
I can see that Outlook loads the DLL and calls DllRegisterServer, and
everything suceeds as expected. However, Outlook then unloads my DLL
(which I think it normally does after registering it), but then it
never loads my DLL again (DllEntryPoint never called). My COM add-in
shows up in the list AND IS CHECKED, but is not actually loaded. If I
close the list and re-open, it is not checked anymore and Outlook says
it had a run-time error at startup. However, it never loaded my DLL
again. My DLL doesn't have any non-system dependencies so I don't
think it is a missing DLL issue (they are all located in system32).

Weird thing is, the same DLL works fine if I enable UAC. Same DLL
also works under other versions of Windows and Office. I know the
easy answer would be to just enable UAC, but that is beyond my control
since it isn't just an in-house project.

Outlook still doesn't require add-ins to be signed, right? I'm
thinking my add-in may not be registered correctly, maybe there are
some new settings as of Office 2007... although why would it work with
UAC enabled, if it was just that.