Errore PHP Catchable fatal error: Impossibile convertire l'oggetto della classe WP_Error in stringa

Ho bisogno di aiuto con questo errore:

PHP Catchable fatal error: Impossibile convertire l'oggetto della classe WP_Error in stringa in /hosting/www/ortopediairati.es/public/wp-content/themes/irati/rt-framework/functions/rt_breadcrumb.php alla riga 58

Ho aggiornato a WordPress 4.8 e il sito non funziona correttamente.

Il file completo è qui:

<?php

/* Funzione RT-Breadcrumb */
function rt_breadcrumb(){
global $taxonomy,$term_slug,$post,$delimiter;

if(!get_option('rttheme_breadcrumb_menus')){
    return false;
}

//Markup 
$before='<div class="breadcrumb">'.wpml_t(THEMESLUG, 'Testo Menu Breadcrumb', get_option(THEMESLUG.'_breadcrumb_text')).' ';
$after='</div>';
$delimiter=' | ';

/* Breadcrumb WooCommerce */
if ( function_exists( 'woocommerce_breadcrumb' ) ) {
    if( is_woocommerce() ){
        $defaults = array(
            'delimiter'  => $delimiter,
            'wrap_before'  => $before,
            'wrap_after' => $after,
            'before'   => '',
            'after'   => '',
            'home'    => null
        );

        woocommerce_breadcrumb($defaults); 
        return false;
    }
} 


echo $before;

//Pagina Home
echo "<a href=\"". BLOGURL ."\" title=\"". get_bloginfo('name')."\">".__( 'Home', 'rt_theme' )."</a>";

// funzione pagine genitore
function page_parents($parent_page_id,$child_pages){
    global $delimiter;

    $parent_page = get_page($parent_page_id);
    $page_parents = $delimiter."<a href=\"".get_permalink($parent_page->ID)."\" title=\"". get_the_title($parent_page->ID) ."\" >". get_the_title($parent_page->ID) ."</a>" .$child_pages;

    if ($parent_page->post_parent) page_parents($parent_page->post_parent,$page_parents);

    else echo $page_parents;

}


// funzione termini genitore
function term_parents($term_id,$child_terms){
    global $taxonomy,$delimiter;

    $parent_term = get_term_by('ID',$term_id, $taxonomy);
    $term_parents = $delimiter."<a href=\"".get_term_link($parent_term->slug,$taxonomy)."\" title=\"". $parent_term->name ."\" >". $parent_term->name ."</a>" .$child_terms;

    if ($parent_term->parent) term_parents($parent_term -> parent,$term_parents);

    else echo $term_parents;

}

//ottieni pagina iniziale
function get_start_page($start_page){
    global $delimiter;

    //pagine genitore di partenza
    $get_start_page=get_page($start_page);
    if ($get_start_page -> post_parent){
        page_parents( $get_start_page -> post_parent,''); 
    }

    //pagina iniziale
    if ($start_page && !get_query_var('lang')) {
        echo  $delimiter."<a href=\"".get_permalink($start_page)."\" title=\"". get_the_title($start_page) ."\" >". get_the_title($start_page) ."</a>";
    }
}

//termini
function term_links(){
    global $taxonomy,$post_type,$term_slug,$delimiter;

    //Trova la pagina iniziale e definisci i nomi delle tassonomie
    if($taxonomy=="product_categories"){
        $start_page=get_option('rttheme_product_list');
    }elseif($taxonomy=="portfolio_categories"){
        $start_page=get_option('rttheme_portf_page');
    }   

    //ottieni pagina iniziale
    if ($start_page) get_start_page($start_page);


    $term=get_term_by('slug',$term_slug, $taxonomy);

    //termini genitore
    if (is_object($term) && $term -> parent){
        echo term_parents($term -> parent,'');   
    } 

    //termine corrente
    if(is_object($term) && $term->slug) echo  $delimiter."<a href=\"".get_term_link($term->slug,$taxonomy)."\" title=\"". $term->name ."\" >". $term->name ."</a>";
}



//Pagine
if ( is_page() ){
    //pagine genitore
    if ($post -> post_parent){
        page_parents( $post -> post_parent,''); 
    } 

    //pagina corrente
    echo  $delimiter ."". $post->post_title;
}

//Singolo
elseif (is_single() && !is_attachment()){ 
    // Ottieni tipo di post
    $post_type = get_post_type();

    //Tassonomie
    if($post_type == 'products' || $post_type == 'portfolio'){

        term_links();
        //pagina corrente
        echo  $delimiter."<a href=\"".get_permalink()."\" title=\"". get_the_title() ."\" >". get_the_title() ."</a>";

    }else{
    //Categorie

    //pagina iniziale
    $start_page=get_option('rttheme_blog_page');

    //ottieni pagina iniziale
    if ($start_page) get_start_page($start_page);

        $category_id = get_the_category();
        $category_id = $category_id[0]->cat_ID;//solo una categoria può essere mostrata nella lista - la prima
        echo $delimiter;
        if($category_id){
            echo get_category_parents($category_id, TRUE, $delimiter, FALSE );
        }
        echo $post->post_title;
    }

//Categoria
}elseif (is_category()){
    //pagina iniziale
    $start_page=get_option('rttheme_blog_page');

    //ottieni pagina iniziale
    if ($start_page) get_start_page($start_page);

        echo $delimiter."".get_category_parents(get_query_var('cat'), TRUE, $delimiter, FALSE);

//Tassonomia
}elseif (is_tax()){
    term_links();
} else {
    echo  $delimiter."";
    wp_title('');
}

echo $after;

wp_reset_query(); 
}
?>

Qualcuno potrebbe aiutarmi?