configuration problem -

[Design75]

define('DIR_WS_ADMIN', '/myadmin/');
  define('DIR_WS_CATALOG', '/zen-cart-v1.5.4/');
  define('DIR_WS_HTTPS_ADMIN', '/myadmin/');
  define('DIR_WS_HTTPS_CATALOG', '/'); 

is in fact not standard 1.5.4 code

this is

  define('DIR_WS_ADMIN', preg_replace('#^' . str_replace('-', '\-', zen_parse_url(HTTP_SERVER, '/path')) . '#', '', dirname($_SERVER['SCRIPT_NAME'])) . '/zen-cart-v1.5.4/');
  define('DIR_WS_CATALOG', '/zen-cart-v1.5.4/');
  define('DIR_WS_HTTPS_ADMIN', preg_replace('#^' . str_replace('-', '\-', zen_parse_url(HTTPS_SERVER, '/path')) . '#', '', dirname($_SERVER['SCRIPT_NAME'])) . '/zen-cart-v1.5.4/');
  define('DIR_WS_HTTPS_CATALOG', '/zen-cart-v1.5.4/'); 

I suggest deleting the configure.php files and rerun the zc_install, and let ZC create the configure files