Some of you may have already noticed this by now, but the logic used to load MAPI providers has changed in Outlook 2013. Previously, we would use LoadLibrary to load a MAPI provider. This API has logic in it to search the user’s PATH for the provider, which is great if you placed the provider somewhere on the user’s PATH. In Outlook 2013, though, we call LoadLibraryEx, passing the LOAD_LIBRARY_SEARCH_DEFAULT_DIRS flag. The effect of this flag is that Outlook no longer searches the path.
Fortunately, you can still put your provider wherever you want by putting the full path in MAPISVC.INF. You may need to rethink how you load your own dependencies, but now that you know what’s going on that problem shouldn’t be insurmountable. BTW – Process Monitor is invaluable in investigating this sort of issue.