The GroupWise Object API (which is what you are using here via Formativ) tends to expose collections using ‘1’ based arrays. This means the first entry has an index of 1.
I would suspect then, that you should be able to access the entries using ‘1’ and ‘2’.
Are you sure you are using the same book, and that the addressBookEntries collection is current?
Don’t forget a ListBox uses ‘0’ based arrays, so the first item has an index of 0, the second 1, etc. You may need to take this into account.