MAPIex uses a custom dll, which interfaces with Outlook directly and has a bunch of custom code on that which makes it incredibly unstable. The Outlook VBO utilizes a dll supplied by Microsoft when you install Outlook, and uses that to interface directly with the program via MAPI.
Other than surface automating, I'm not sure what to tell you. The only time I've seen Outlook pop up a message like that was for programmatic access. I recall you saying you used a macro before, which might have something to do with it (but I'm just grasping at straws here). You could launch Outlook as admin and go through the Trust Center options, making sure 'Macro Settings' and 'Programmatic Access' are set to allow, but that's all I've got.