possible typo: form_set_error("taxonomy[tags][$vid",

/**
 * Make sure incoming vids are free tagging enabled.
 */
function taxonomy_node_validate(&$node) {
  if ($node->taxonomy) {
    $terms = $node->taxonomy;
    if ($terms['tags']) {
      foreach ($terms['tags'] as $vid => $vid_value) {
        $vocabulary = taxonomy_get_vocabulary($vid);
        if (!$vocabulary->tags) {
          form_set_error("taxonomy[tags][$vid", t('The %name vocabulary can not be modified in this way.', array('%name' => theme('placeholder', $vocabulary->name))));
        }
      }
    }
  }
}

I'm not sure, but it looks like a typo on line 725 of taxonomy.module:
form_set_error("taxonomy[tags][$vid", t('The %name vocabulary can not be modified in this way.', array('%name' => theme('placeholder', $vocabulary->name))));