Need to change node's path to CCK value
I think what you should be doing is something along the lines of the following:

  $node=$vars['node']; // or however you get the node object

  $source = 'node/' . $node-&gt;nid;
  $alias = $node-&gt;field_se_news_source['und'][0]['url'];

  if (!empty($alias) {
    $paths=array('source' =&gt; $source, 'alias' =&gt; $alias);
    path_save($paths);
  }


but I would do in it hook_node_presave() instead.

Also be aware that I imagine this won't work if the url in your CCK field is not local to the host system.

More info:

http://api.drupal.org/api/drupal/modules%21node%21node.api.php/function/hook_node_presave/7

http://api.drupal.org/api/drupal/includes!path.inc/function/path_save/7

And oh, the error is because you were passing path_save() the return value of the array() constructor and not an actual variable.