Fatal error: Unsupported operand types

I'm getting the following error message when I try to refresh a Leech feed:

Fatal error: Unsupported operand types in /usr/www/users/dpedia/drupal5/sites/all/modules/yahoo_terms/yahoo_terms.module on line 123

The path that generates this error message is:

leech/refresh/45?destination=leech/feed

The code that generates this error is as follows (beginning with line 118):

  $tids = _yahoo_terms_create_vocabulary_items($terms, $vid, $static);
  $tids_in_node = array_keys($node->taxonomy);
  $tids_fetched = array_keys($tids);
  // Union of these arrays
  $tids_now = $tids_in_node + $tids_fetched; 
  taxonomy_node_save($node->nid, $tids_now);

I checked the variable table in my database, and it has a value of "4" (the numeric ID for my "keywords" vocabulary) for yahoo_terms_vocab, yahoo_terms_vocab_for_rssfeed (rssfeed is the content type for my feed items) and yahoo_terms_vocab_for_rsssource (the content type for my feed sources). I inserted a line into the module just above the lines above to set $vid = 4, and the error message disappeared. It appears, therefore, that the $vid is not getting passed into this function properly. I believe the place where this is happening is line 2364 of the leech module, which reads,

      node_invoke_nodeapi($edit, "terms_tagging", $vid, $query);

If I add a "$vid=4" just above the node_invoke_nodeapi command, the fatal error disappears, but some other strange things are happening. When I click on "retrieve feed items" for one of my feed sources, items get loaded and nodes get created, but the items don't show up when I click "view feed items." However, they do show up as items under taxonomy/term/1, which is strange, because taxonomy/term/1 is a term in my "topics" vocabulary, not the "keywords" vocabulary which I am trying to use with leech/yahoo_terms.