Show results for multiple page-types

You should use ‘meta_query’ instead it is a array of arrays

$product_pages_args = array(
    'meta_query' => array(
      array(
       'key' => '_wp_page_template',
       'value' => array('page_library_html_content.php',page_library_css_content.php') ,
       'compare' => 'IN'
    ), 
    )
)

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)