In Provider.cpp, you return MAPI_E_UNCONFIGURED when the user cancels the PST path selection dialog.  This appears to confuse Outlook and causes several more dialogs to appear.  Returning MAPI_E_USER_CANCEL instead appears to fix the problem.

Also, the return value from SetOfflineStoreProps, the function that displays the open dialog, isn't checked before calling lpProfSect->GetProps on the line below.  I'm not sure whether that's intentional.