Try leaving Object class blank until logins are working. When they are you can try restricting who can log in by adding the filter for security groups.
- Contexts: should be the DN of the OUs containing the users who should have access to Moodle.
- User attribute: should be "sAMAccountName" as stated in the documentation.
- Member attribute: leave this blank.
Presumably you've used the Test settings link and enabled the plugin:
If you know PHP I wrote a command line script, ldap_test.php, to help troubleshoot these settings. You need to set the following values (see lines 41-53):
define('ATTRIBUTES', 'sAMAccountName, givenName, sn, mail');
If Use TLS is off change line 53 to:
Run it with php ldap_test.php, it should return the accounts from AD if these settings are correct. It may help determine the settings needed for Moodle (more information). Alternatively you can use ldapsearch.