how to load page b using expander in page a?

as you know, we can use this code in index and it works truely... it loads the page_userreferals...

$g->addColumn('expander','userreferals',"Users List");

but when I use it in other pages, an error occurs...

Exception_PathFinder, code: 0

Additional information:

    file: desk\Page\userreferals.php
    type: page
    attempted_locations:
        0: C:/wamp/www/test/page/desk/userreferals.php
...

the problem is that the agile tookit search for the requested page in subdirectory. how can we change that?

try:

$grid->columns['userreferals']['page'] = $this->api->url('b');