The {2} expression for the {0} {1}' refers to the global variable OverallPageNumber or OverallTotalPages in an aggregate ...

The {2} expression for the {0} ‘{1}' refers to the global variable OverallPageNumber or OverallTotalPages in an aggregate function that specifies a dataset scope.  These global variables cannot be used with an aggregate function that has a dataset scope in a page header or page footer.