Plugin for Postbil_legacy - show number of custom photo records for each member

[fabioski]

In my forum each member can post photos with a customized page. I save in a Database table photo infos (member who upload photo, title, kb of photo, etc).

I want to display under avatar a link to personal member photo page. I am able to do this with this plugin created for postbit_display_complete:

// Utente di riferimento del post
$obj_userid = $post[userid];
$obj_username = $post[musername];

$testo_libri .= "<div><a title=\"Libreria personale utente $obj_username\" href=\"http://www.forumlibri.com/libri/my-$obj_userid/index.html\">Libreria personale $obj_username</a></div>";

I also want to show in the link THE NUMBER OF UPLOAD PHOTO for each member.
I try to use this query in the same plug-in:

// calcolo il numero di libri nella libreria personale
$numerolibri = $db->query_first_slave("
    SELECT *
    FROM tab_mylib
    WHERE myl_userid = '1'
");

But VBulletin show me this error:

Fatal error: Call to a member function query_first_slave() on a non-object in /var/www/web157/html/forum/includes/class_postbit.php(293) : eval()'d code on line 8

How can I obtain the number of uploaded photos for each member and show it under the avatars space?