add_rewrite_tag error when trying to use wp_insert_post in a third party applica

as the title says, i get the dreaded

Fatal error: Call to a member function add_rewrite_tag() on a non-object

when i try to use wp_insert_post in a whmcs hook. i have tried to make sure my register_taxonomy is correct and as far as i can tell it is.. here the whole thing is:

add_action( 'init', 'create_car_taxonomies', 1 );

//create three taxonomies, Makes, Classes and Features for the post type "cars"
function create_car_taxonomies()
{
  // Add new taxonomy, make it hierarchical (like categories)
  $labels = array(
    'name' => _x( 'Types', 'taxonomy general name' ),
    'singular_name' => _x( 'Type', 'taxonomy singular name' ),
    'search_items' =>  __( 'Search Types' ),
    'all_items' => __( 'All Types' ),
    'parent_item' => null,
    'parent_item_colon' => null,
    'edit_item' => __( 'Edit Type' ),
    'update_item' => __( 'Update Type' ),
    'add_new_item' => __( 'Add New Type' ),
    'new_item_name' => __( 'New Type' ),
  );

  register_taxonomy('type',array('website'), array(
    'hierarchical' => true,
    'labels' => $labels,
    'show_ui' => true,
    'query_var' => true,
    "capabilities" => array('manage_terms','edit_terms','delete_terms','assign_terms'),
    'rewrite' => array( 'slug' => 'business-type' ),
  ));

  // Add new taxonomy, NOT hierarchical (like tags)
  $labels = array(
    'name' => _x( 'Features', 'taxonomy general name' ),
    'singular_name' => _x( 'Feature', 'taxonomy singular name' ),
    'search_items' =>  __( 'Search Features' ),
    'popular_items' => __( 'Popular Features' ),
    'all_items' => __( 'All Features' ),
    'parent_item' => null,
    'parent_item_colon' => null,
    'edit_item' => __( 'Edit Feature' ),
    'update_item' => __( 'Update Feature' ),
    'add_new_item' => __( 'Add New Feature' ),
    'new_item_name' => __( 'New Feature Name' ),
    'separate_items_with_commas' => __( 'Separate features with commas' ),
    'add_or_remove_items' => __( 'Add or remove features' ),
    'choose_from_most_used' => __( 'Choose from the most used features' ),
    'not_found' => __('No features found')
  );

  register_taxonomy('features','website',array(
    'hierarchical' => false,
    'labels' => $labels,
    'show_ui' => true,
    'query_var' => true,
    "capabilities" => array('manage_terms','edit_terms','delete_terms','assign_terms'),
    'rewrite' => array( 'slug' => 'feature' ),
  ));

}

any ideas what is going on?