explain load_node_by_type function better

this works for me:

    <?php $children = nodefamily_relation_load($nid); ?>
    <?php
      foreach ($children as $childnode) {
        print node_view($childnode);

this does not, and produces the following warnings:

    <?php $children = nodefamily_relation_load_by_type($nid); ?>
    <?php
      foreach ($children as $childnode) {
        print node_view($childnode);

warnings:

warning: Invalid argument supplied for foreach() in C:\home\user\public_html\drupal\modules\node\node.module on line 504. 
warning: implode() [function.implode]: Bad arguments. in C:\home\user\public_html\drupal\modules\node\node.module on line 508. 
user warning: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '' at line 1 query: SELECT n.nid, n.vid, n.type, n.status, n.created, n.changed, n.comment, n.promote, n.sticky, r.timestamp AS revision_timestamp, r.title, r.body, r.teaser, r.log, r.format, u.uid, u.name, u.picture, u.data FROM node n INNER JOIN users u ON u.uid = n.uid INNER JOIN node_revisions r ON r.vid = n.vid WHERE in C:\home\user\public_html\drupal\includes\database.mysql.inc on line 172. 
warning: Invalid argument supplied for foreach() in C:\home\user\public_html\drupal\themes\jolly\node.tpl.php on line 31. 

I am doing something wrong, or is this some kind of bug?

thanks,
abramo