wp-includes/general-template.php:2102 is the function wp_admin_css().
On the login page this function is called in login_header().
Your theme or some plugin trys to send an HTTP header after that, probably during the actions login_enqueue_scripts or login_head.
wp-includes/option.php on:569 is in function wp_user_settings(); a cookie is set here. Cookies are HTTP headers, so that cannot work when there was already some output.
Search for something like …
add_action( 'login_head', 'some_function_name' );
… and the registered callback function is probably calling wp_user_settings().