General help

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.

Other fields:

• 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('HOST_URL', 'example.com');
define('BIND_DN', 'service-acct@example.com');
define('BIND_PW', 'password');
define('CONTEXTS', 'dc=example,dc=com');
define('FILTERS', '(objectClass=user)');
define('ATTRIBUTES', 'sAMAccountName, givenName, sn, mail');

If Use TLS is off change line 53 to:

define('STARTTLS', false);

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.