With the PageList button you can show a list of non visible pages,
the list of available pages is shown via a popup menu. Therefore you need to assign a popup menu instance that will be used to show this list of closed pages via the property AdvOfficePager.PageListMenu.
This is also explained in the developers guide: http://www.tmssoftware.biz/Download/Manuals/TMS%20TAdvOfficePager.pdf