I've got a user that is reporting an error as follows when sending mail:

Debug Assertion Failed!
Program: <snip>Outlook.exe
File: C:\src\frank\mapi\src\sharingadding\addin.cpp
Line 1605

Expression g_pAddinInstance
etc.

What is the best way to go about debugging what could be going wrong here? I've recreated the outlook profile and the error still comes about. It is only when sending mail via the normal procedure, but if you hit ignore on the debug box you can actually get mail to send out. He also states that if you initiate the mail from, for example, Excel doing a mail spreadsheet, it works fine. I did grab some debug logs from a clean login, send attempt, program close.