I happened to notice when I was investigating a user's problem that includes/auth/auth_ldap.php has a bad return on line 159:

[code] return $user->lang['LDAP_NO_SERVER_CONNECTION'];[/code]

which translates to
[code] 'LDAP_NO_SERVER_CONNECTION' => 'Could not connect to LDAP server.',[/code]

the login_box function is expecting an array to be returned, not a string as this file is doing on line-145:

[code] return array(
'status' => LOGIN_ERROR_EXTERNAL_AUTH,
'error_msg' => 'LDAP_NO_SERVER_CONNECTION',
'user_row' => array('user_id' => ANONYMOUS),
);[/code]