How to catch an error when running drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL)?

Question

Drupal

There is a migration script from d5 to d7.
It worked stably and at some point stopped connecting drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL), rolled back the changes that I made in the migration, but still not loading .. there is no database backup.
Connection:
define('DRUPAL_ROOT', getcwd());
require_once DRUPAL_ROOT . '/includes/password.inc';
require_once DRUPAL_ROOT . '/includes/bootstrap.inc';
include_once DRUPAL_ROOT . '/includes/mail.inc';
drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);
How to catch an error or in which direction to look at all?