LDAP on - login screen displays anyway

[matroos]

I have been trying to get LDAP to work during the past weeks, but then gave up a while ago.

My issue: got it to work at some point, but as I have an error in the log when LDAP was enabled, I switched back to manual "on screen" login.

But now, with LDAP enabled again in the config file, I am transferred to the login page for manual user/password login...

I have these settings in my config file:
# --- Authentication method ---
$g_login_method = 'LDAP';
$g_ldap_server = 'LDAP://PXGBSSC2DCG004.bsg.LOCAL:389';
$g_ldap_root_dn = 'dc=bsg,dc=LOCAL';
$g_ldap_protocol_version = 3;
$g_ldap_follow_referrals = 'OFF';
$g_ldap_uid_field = sAMAccountName;
$g_log_level = LOG_LDAP;
$g_log_destination = 'file:D:\MantisBT\mantisbt.log';

When I used that config, a few weeks ago, it worked - half... That is, I saw this in the log:
2020-03-03 17:23 CET LDAP ldap_api.php:327 ldap_authenticate_by_username() Binding to LDAP server
2020-03-03 17:23 CET LDAP ldap_api.php:63 ldap_connect_bind() Attempting connection to LDAP server/URI 'LDAP://PXGBSSC2DCG004.bsg.LOCAL:389'.
2020-03-03 17:23 CET LDAP ldap_api.php:66 ldap_connect_bind() Connection accepted by LDAP server
2020-03-03 17:23 CET LDAP ldap_api.php:79 ldap_connect_bind() Setting LDAP protocol version to 3
2020-03-03 17:23 CET LDAP ldap_api.php:105 ldap_connect_bind() Attempting anonymous bind to ldap server
2020-03-03 17:23 CET LDAP ldap_api.php:114 ldap_connect_bind() Bind to ldap server successful
2020-03-03 17:23 CET LDAP ldap_api.php:335 ldap_authenticate_by_username() Searching for (&(sAMAccountName=clambert))
2020-03-03 17:23 CET LDAP ldap_api.php:46 ldap_log_error() ERROR #1: Operations error
2020-03-03 17:23 CET LDAP ldap_api.php:340 ldap_authenticate_by_username() ldap search failed

So, that tells me a few things:
- LDAP setup seems to be OK.
- LDAP authentication with my AD user name seems to fail.

Extra information: I have been using a previous version of MantisBT. The new version, to which I have upgraded (2.23) does not support the old way of using AD login anymore (plugin), I needed to find a solution via LDAP. Could it be that the user table in the MantisBT database is not "compatible" in some way, with the "new" LDAP method I want to use?

[cas]

The old plugin, is that adLogin?
If so, what error message do you get?