I am trying to determine which Page of the Pageeframe has the focus.

In addition to what the others have said, remember that the activePage property is corresponds to the PageOrder property of the page that currently has fous. So, to be absolutely positively sure you have the right page, you need code that is similar to this in the pageframe:

FOR EACH loPage IN This.Pages
  IF loPage.PageOrder = This.activePage
    *** loPage is the object reference to the page that has focus
    .
    .
    .
    EXIT
  ENDIF
ENDFOR